NAS Servers: specifications, types

— Rack mounted. In accordance with the name, this type of NAS-servers is designed for installation in telecommunications racks. These devices come in standard sizes and mounts for quick and easy installation in a standard equipment slot. Technically, the possibility of a separate installation is not excluded, however, it is inconvenient and hardly justified to use such models outside the racks. Typically, this form factor includes the most advanced professional NAS servers that can carry up to 12 drives (see "Drive Slots") and have an extensive set of software features, including regarding RAID (see the relevant paragraphs below for more details).

— Desktop. This category includes NAS servers installed separately — on a table, shelf, floor, etc.; roughly speaking — all models for which rack mounting is not provided. Among desktop models there are models of any price level, from modest low-cost devices to advanced professional solutions with the appropriate capabilities.

The number of slots for drives in the form factor 3.5", provided in the design of the server.

Initially, 3.5 "is the traditional, most popular form factor of drives for server systems. It is noticeably larger than 2.5", but it allows you to create capacious, inexpensive (in terms of gigabytes) and reliable media, in which it is also easier to implement various additional functions. That is why, specifically in NAS servers, this form factor is also the most popular; slots under 2.5" are much less common in such equipment, and in most cases they complement 3.5".

As for the number of slots, it can vary from 2 (or even 1) in the most basic desktop systems to 8 or more in professional rack-mount solutions. And not only their maximum capacity depends on the specific number of drives, but also some other features of work — first of all, the physical possibility of using one or another RAID level.

The number of slots for drives in the form factor 2.5", provided in the design of the server.

This form factor was originally developed for laptops as a more compact alternative to the "desktop" 3.5". Nowadays, it is increasingly used in desktops, but such media (and slots for them) have not received distribution in server systems. This is due with the fact that the consequence of the small size is a number of disadvantages: lower capacity, higher cost (in terms of gigabytes), the complexity of using special functions, and for classic hard drives — also relatively low reliability. That is why 2.5 "slots in NAS- servers are relatively rare and in small quantities. At the same time, in some models it is 1 – 2 bays, complementing the set of 4 or more 3.5" slots and used for SSD modules operating in the high-speed buffer format. In others, the number of 2.5" slots may not differ much from the number of 3.5" bays — this provides overall versatility, allowing you to install different formats of drives at the same time. There are also solutions only for 2.5" — these are single ultra-compact models with a desktop installation; in them the number of such compartments can reach 8.

The total capacity of all drives supplied with the NAS server (see "Preinstalled Drives"). In some situations, it is more convenient to use a ready-made solution than to independently equip an “empty” server with disks; Knowing the volume of pre-installed drives, you can evaluate how this or that model is suitable for your purposes.

Note that the specifications usually indicate the usual amount of disk volumes installed on the NAS server. At the same time, some RAID levels significantly reduce the available volume; see "RAID support" for details.

This item characterizes the maximum capabilities of the device for connecting drives. This way you can understand how much maximum memory can be added to the NAS server.

The ability to remove one of the NAS server's internal drives and replace it with another without shutting down the entire server. Thanks to this, time is not wasted on rebooting, and the information on other media remains constantly available. Note that even if this feature is available in the NAS server, it may not be available when using RAID — some versions of this technology (see "RAID support") do not allow hot- plugging drives.

NAS server support SATA 2 standard. As the second version of the SATA interface designed for connecting internal drives, this standard is one of the most popular today. The practical data transfer rate is in the order of 2.4 Gbps (300 Mbps). Note that SATA 2 servers are compatible with peripherals designed for other versions of SATA (both earlier and later versions); the only thing is that the speed with such a connection will be limited by the capabilities of the slower version.

The third version of the SATA standard used in computer technology to connect internal drives. It differs from the previous version of SATA 2 (see above) in an increased data transfer rate — about 5.9 Gbps (600 MB / s) in fact — as well as a number of optimizations in power consumption. Even earlier drives can be connected to SATA 3, however, the speed of operation with such a connection will be limited by the characteristics of the drive itself.

The presence of a SAS interface in the NAS server. SAS is a version of the SCSI interface (so-called Serial Attached SCSI) used to connect internal drives and is found today mainly in server systems. Note that specialized server hard drives, which have increased volume, speed and time between failures, can be equipped with this particular connection interface; and therefore, if you want to use such components, it is best to take a server with SAS. The connection speed on this interface is up to 6 Gbps (750 Mb / s), in the future it is possible to double it.

The number of M.2 connectors provided in the design of the NAS server.

The M.2 connector is used to connect various internal peripherals, mostly miniature form factor. Note that two electrical (logical) interfaces can be implemented through this connector — SATA 3.0 and PCI-Express, and each individual M.2 socket on the board can support both of these interfaces at once, or only one of them. These nuances should be clarified before buying, since the possibilities for using M.2 directly depend on them. So, with support for SATA 3.0, such a connector is intended exclusively for drives, and the speed of SATA is noticeably lower than that of PCI-E; so this M.2 variant is mostly used by inexpensive SSD modules. In turn, PCI-E is somewhat more expensive, but it is faster and more versatile. Support for this interface allows you to connect both high-end SSDs and various expansion cards (for example, sound cards or internal wireless adapters) to the NAS server.

The number of PCI-E slots provided in the design of the NAS server.

PCI-E is one of the most popular modern interfaces for connecting internal components to a computer motherboard. Specifically, in NAS servers, it can be used, in particular, for wireless adapters and SSD drives; in the latter case, PCI-E allows higher speeds than SATA and fully realizes the potential of solid-state memory. And the number of such connectors corresponds to the number of PCI-E components that can be simultaneously installed in the server.

Note that the PCI-E connection can use a different number of lines (1x, 4x, 16x), and for normal operation it is necessary that the slot on the "motherboard" has no fewer lines than the installed component. In fact, this means that a component with a 1x connector will easily fit into any slot, but with a larger connector, the connection should be specified separately. However, in the case of NAS servers, even PCI-E 4x capabilities are rarely required, not to mention 16x.

NAS server supports RAID technology. The term is an abbreviation for "redundant array of independent disks", that is, "redundant array of independent disks". Accordingly, only models with more than one drive slot can have this feature (see “Drive Slots”).

There are several options for combining disks into a redundant array, they differ in a number of characteristics: some focus on increasing speed, others focus on fault tolerance. However, all RAIDs have two key differences from non-arrayed systems. The first is that the RAID array is perceived by the system as one single drive. The second is “redundancy”: the total volume of disks included in the array must be greater than the volume of data that is planned to be stored on them. This is due to the fact that the array uses service information, which must be stored on the same disks (however, the exception is RAID 0, see below).

The most common RAID versions today are:

— RAID 0. An array of two or more disks, information on which is written by interleaving: first, the data is divided into blocks of the same length, and then each of these blocks is written to its “own” disk in turn. For example, if a RAID 0 array consists of 3 disks, and the file is divided into 7 parts, then parts 1, 4 and 7 will be on the first disk, 2 and 5 on the second, and 3 and 6 on the third. that it is not actually a RAID, as it devoid of "redundancy" — the volume of the array corresp...onds to the sum of the disk volumes. The main advantage of RAID 0 is a significant increase in performance; it is higher, the more disks are included in the array. On the other hand, the reliability of such systems is lower than that of individual drives: in the event of a failure of any of the drives, the entire array becomes inaccessible, and the more drives are used, the higher the likelihood of this. The minimum number of drives for RAID 0 is two.

— RAID 1. In arrays of this type, information is recorded according to the principle of mirroring: two disks, the information on which is completely identical. This provides a very solid system fault tolerance: the data contained in the array will be available in full, without additional tricks and serious drops in performance, even if one of the disks fails completely. In addition, some gain in read speed is achieved in this way, and "hot swapping" (see above) usually does not cause problems. The disadvantage is the high cost of building: you have to pay for two hard drives, getting the volume of one. However, in some cases this can be quite an acceptable price for increased reliability.

— RAID 5. In such arrays, unlike RAID 0 and 1 (see above), not only basic information is stored on disks, but also service information — in the form of data for error correction (so-called checksums). In this case, both types of information are distributed evenly across all disks. For example, in RAID 5, consisting of 4 disks, the first "portion" of data to be written will be divided equally between disks 1,2 and 3, and the checksum will be written to disk 4; the second portion is between disks 1,2 and 4, with a checksum written to disk 3, etc. This provides good fault tolerance: the array provides data access in the event of a complete failure of any of the drives. In addition, RAID 5 is characterized by a very low level of redundancy: the working volume of the array is equal to the volume of the smallest disk multiplied by (n-1), where n is the total number of disks. The main disadvantages of RAID 5 are relatively low performance, which drops even more in the event of a failure; this is due to the abundance of additional operations associated with the use of checksums. In addition, if one of the drives fails, the reliability of the remaining array is reduced to the RAID 0 level (see above), and the remaining drives experience very significant loads, which further increases the risk of additional failure; if two disks fail, data can be recovered only by special methods. The minimum required number of drives for RAID 5 is three.

— RAID 10. A combination of arrays of the RAID 0 and RAID 1 types (see above): the disks are combined in pairs into mirror RAID 1 arrays, and the whole system operates on the RAID 0 principle, with sequential information writing to each pair of disks. This scheme allows you to maintain the high performance characteristic of the classic RAID 0, while eliminating its main drawback — unreliability. Regardless of the number of drives, a RAID 10 array is completely insensitive to a single drive failure and can easily survive the loss of half the drives if they are all in different mirrored pairs. At the same time, the simultaneous failure of one pair leads to an irreversible loss of information. Another drawback is the high redundancy characteristic of RAID 1: the useful volume of the array is half the sum of the volumes of all disks. At least 4 drives are required to build RAID 10, and anyway, their number must be even.

— JBOD. Abbreviation for "Just a bunch of disks" — "just a bunch of disks." This name, although rough, but quite accurately describes the features of arrays of this type: JBOD does not provide "redundancy", does not use additional technologies such as checksums (see RAID 5), and the volume of the array is equal to the total volume of all disks included in it. The discs are connected in a kind of series. This means that when writing each next file, the remaining free space on the previous disk in the queue is first filled, and if there is not enough space, the rest of the data is written to the next one. For example, if you write two 70 GB files to an empty JBOD array of 100 GB disks, the first file will fit entirely on the first disk, and the second will take up the remaining 30 GB on the first and 40 GB on the second. Similarly, if the volume of the file exceeds the volume of the entire disk — in our example, a 120 GB file will occupy the entire first disk and 20 GB on the second. The advantages of JBOD are good performance with a small load on the processor and the ability to combine disks with different sizes and speeds. In addition, they are somewhat more fault-tolerant than similar RAID 0 in many respects (see above): the failure of one disk does not necessarily lead to the irreversible loss of data of the entire array. At the same time, the reliability of JBODs is still somewhat lower than that of single disks, and therefore they can only be considered as a tool for improving performance.

Note that the variety of RAID standards used in modern NAS servers is not limited to the above. Additional options may include but are not limited to:

— RAID 3 and RAID 4 — similar to RAID 5 described above, however, in these formats, checksums are written to one dedicated disk, and are not distributed evenly across all disks. This improves performance (for RAID 3 — only in some cases), but reduces the reliability of the control disk. For a number of reasons, they are rather uncommon.

— RAID 6 is another analogue of RAID 5, differs in that it uses not one, but two sets of checksums, also evenly distributed over all disks. This significantly increases reliability, but reduces performance and increases the level of redundancy — the volumes of not one, but two disks “fall out” of the total volume.

— RAID 0+1. It can mean 2 options. The most common is an array of two RAID 0 (striped) combined into a RAID 1 (mirror). Some manufacturers use RAID 0+1 as a designation for an advanced technology that allows you to “mirror” information on an odd number of disks: for example, in a three-disk array, the first piece of data will be mirrored on disks 1 and 2, the second — on 2 and 3, the third — on 3 and 1 etc.

— RAID 50 and RAID 60. RAID 5 and RAID 6 arrays, respectively, composed of groups of disks combined in RAID 0. Provide high reliability and performance, but are expensive and difficult to maintain.

There are also other options for "combined" RAID — for example, in RAID 51, two RAID 5 arrays are made into a "mirror" pair.

The number of LAN ports provided in the design of the NAS server.

LAN — a connector used for a wired connection to Ethernet local networks (the most common "local" format today, it is also used to access the Internet). For a relatively simple network (say, within a medium office), one LAN port will be enough. However, models are produced where there are more than one such ports, mainly 2 and 4 connectors. They are designed for large networks divided into subnets with separate access to the NAS server: the presence of several LAN connectors allows you to connect each of the subnets directly without using a router. This simplifies the network architecture and optimizes the load.

The maximum operating speed supported by the LAN port(s) of the NAS server. For the LAN ports themselves, see above; in today's networking equipment, higher speed means compatibility with lower rates

In general, the higher the LAN speed, the wider the bandwidth, the faster the device will cope with data transfer and the easier it will be for it to work with several network requests at once. As for specific standards, 1 Gbps is the most popular nowadays: it gives quite decent speed and at the same time is inexpensive. The more advanced 10 Gbps standard is less common, mostly in professional equipment designed for high loads. The middle and rare link are models with a speed of 2.5 Gbps. But LAN 100 Mbps is considered completely obsolete version.

The number of SFP ports provided in the design of the NAS server.

The SFP standard itself covers different types of connections, but in this case, connectors for high-speed fibre optic cable are usually meant. The data transfer rate via SFP can reach tens of gigabits per second; such a connection is used in professional network equipment.

The number of SFP+ ports provided in the design of the NAS server.

Initially, the SFP standard provides several types of connection, but in this case we are usually talking about connectors for fibre optic cable. And SFP + is an improved version of the original SFP — in particular, the data transfer rate in this standard can reach 16 Gbps. In addition, a common advantage of fibre optic connections is complete insensitivity to electromagnetic interference. However, support for this standard affects the cost of the device, despite the fact that in domestic use the described features are generally not needed. Therefore, the presence of SFP + is typical mainly for professional servers, and even in them the number of such connectors does not exceed two.

The number of USB 2.0 ports provided in the design of the NAS server.

USB connectors are used in computer technology to connect various external peripherals. In the case of NAS servers, we are most often talking about external drives — flash drives, hard drives, etc. In this way, you can transfer information from an internal drive to an external one (for example, for backup purposes) or vice versa, and even expand the total working volume of the server . In addition, on models with a VGA output (see below), a keyboard can also be connected to USB, and on models with a print server function (see "Software Features"), respectively, a printer. For added convenience, the USB connector can be placed on the front panel (see below).

As for USB 2.0 specifically, today this version is generally considered obsolete due to the relatively low speed (up to 480 Mbps) and the low power supplied through the connector. Peripherals of newer versions can be connected to such a port, however, the speed will be limited by the capabilities of version 2.0, and the power supply may not be sufficient. Therefore, in modern NAS servers, such connectors are quite rare — mainly as an addition to the newer and faster USB 3.2 gen1 (see below), designed for relatively unpretentious peripherals like keyboards.

The number of USB 3.2 gen1 ports provided in the design of the NAS server.

USB connectors are used in computer technology to connect various external peripherals. In the case of NAS servers, we are most often talking about external drives — flash drives, hard drives, etc. In this way, you can transfer information from an internal drive to an external one (for example, for backup purposes) or vice versa, and even expand the total working volume of the server . In addition, on models with a VGA output (see below), a keyboard can also be connected to USB, and on models with a print server function (see "Software Features"), respectively, a printer. For added convenience, the USB connector can be placed on the front panel (see below).

Specifically, USB 3.2 gen1 (formerly known as USB 3.0 and USB 3.1 gen1) is the direct successor to USB 2.0 and is the most common USB standard today. This version provides data transfer rates up to 4.8 Gbps, as well as a fairly high power supply. At the same time, such connectors are backward compatible with peripherals using USB 2.0.

The number of USB 3.2 gen2 ports provided in the design of the NAS server.

USB connectors are used in computer technology to connect various external peripherals. In the case of NAS servers, we are most often talking about external drives - flash drives, hard drives, etc. In this way, you can transfer information from an internal drive to an external one (for example, for backup purposes) or vice versa, and even expand the total working volume of the server . In addition, on models with a VGA output (see below), a keyboard can also be connected to USB, and on models with a print server function (see “Software Features”), respectively, a printer. For added convenience, the USB connector can be placed on the front panel (see below).

Specifically, USB 3.2 gen1 (formerly known as USB 3.1 and USB 3.1 gen2) is the direct successor to USB 2.0 and is the most common USB standard today. This version provides data transfer rates up to 10 Gbps, as well as a fairly high power supply. At the same time, such connectors are backward compatible with peripherals using USB 2.0.

The number of USB-C ports provided in the design of the NAS server.

Like the more traditional USB 2.0 and USB 3.2 gen1 (see above), connectors of this type are mainly used to connect external peripherals: drives for exchanging data and/or expanding the working volumes of a NAS server, keyboards for direct control, etc. However, USB-C has its own specifics. First of all, this is the design of the connector: it has small dimensions (slightly larger than microUSB) and a two-sided design (the plug can be connected on either side, unlike previous standards). The second feature is that other interfaces can be implemented through the physical USB-C connector — for example, Thunderbolt, which also has a video output mode. However, the main format for this type of port is still the connection of USB devices; in terms of capabilities, such a connection most often corresponds to USB 3.2 gen1 (at speeds up to 4.8 Gbps) or USB 3.2 gen2 (up to 10 Gbps).

For added convenience, the USB-C connector can be placed on the front panel (see below).

The number of Thunderbolt connectors, as well as their version, provided in the design of the NAS server.

Thunderbolt is a universal high-speed interface primarily known from Apple laptops, but used by other manufacturers as well. Such a connection actually combines several interfaces — at least PCI-E for peripherals and DisplayPort for outputting video (and audio) to external screens, and others in recent versions. Thanks to this, Thunderbolt can be used both as a peripheral connector and as a video output. Even greater versatility of this interface is provided by the daisy chain function — serial connection of several devices (up to 6) to one port; moreover, it can be both monitors and other peripherals, and in Apple technology, other “apple” computers. Thus, a small number of connectors can be compensated by serial connection.

— Thunderbolt 3. Version introduced in 2015. In this generation, developers have abandoned the DisplayPort connector in favor of the more versatile USB-C. Thus, the Thunderbolt v3 connection is often implemented not as a separate connector, but as a special mode of operation of the regular USB-C port. Power Delivery support is also an optional, but very common feature. , which allows you to supply connected devices with power up to 100 W through the same cable. The data transfer rate can reach 40 Gbps, however, note that with a wire length of more than 0.5 m, a special active cable may be required to maintain this speed. Howev...er, conventional passive USB-C cables are also suitable for working with Thunderbolt v3 — except that the speed may be noticeably lower than the maximum possible (albeit above 20 Gbps, which runs USB 3.2 gen2).

Thunderbolt v4. The latest (at the end of 2020) version of this interface, presented in the summer of the same year. It also uses a USB-C connector. Formally, the maximum throughput remains the same as its predecessor — 40 Gbps; however, a number of improvements have significantly increased the actual connectivity. Thus, Thunderbolt v4 allows you to broadcast a signal simultaneously to two 4K monitors (at least) and provides a data transfer rate according to the PCI-E standard of at least 32 Gbps (against 16 Gbps in the previous version). In addition, this interface is mutually compatible with USB4 by default, and the daisy chain function is supplemented by the ability to connect hubs with up to 4 Thunderbolt v4 ports. Other features include protection against DMA (direct memory access) attacks.

The number of eSATA connectors provided in the design of the NAS server.

eSATA is a specialized interface for connecting external drives, primarily hard drives. It provides data transfer rates up to 2.4 Gbps — half that of USB 3.2 gen1, but significantly more than USB 2.0. And the clear advantage of such an interface is that it allows you to leave free USB ports that may be required for other devices. At the same time, eSATA drives are not very common nowadays, therefore, connectors of this type are provided in NAS servers quite rarely (and mostly in an amount of less than one).

Built-in slot for reading memory cards — most often SD standard.

Memory cards are supported by almost all modern laptops and cameras, most action cameras, as well as pocket gadgets like smartphones and tablets. So, a NAS server with a card reader will be convenient, first of all, if you plan to frequently exchange data with such devices — for example, copy the captured photos from the camera. Note that pocket devices usually use a smaller version of SD cards — microSD, however, such cards are also compatible with SD slots when using appropriate adapters.

Connector for outputting video signal to an external screen. Allows you to connect a monitor to the NAS server and monitor the operation parameters on it; and some models even have firmware with a full graphical interface, allow keyboard and mouse connection, and can be controlled directly from the monitor and keyboard/mouse. However, it is worth noting that VGA uses an analogue format, supports relatively low resolutions (in fact, up to 1280x1024) and does not provide sound transmission. Therefore, nowadays it is rare, as it is gradually being replaced by more advanced video interfaces — primarily HDMI (see below).

The presence of an HDMI output in the NAS server; either the presence of such a connector itself or its specific version can be indicated here.

HDMI is a digital interface specifically designed to carry high-definition video and multi-channel audio. This is the most common of these interfaces, most modern monitors, TVs, home theaters, projectors, etc. have this type of input. Thus, even in such a specific technique as NAS servers, such outputs have several applications. The first option is to connect a monitor to monitor the parameters of the server; some devices at the same time allow you to connect keyboards / mice and control the server directly, like a regular computer. The second option is to use the NAS server as a media centre to broadcast movies and other content to a TV, home theater, etc.

The specific functionality of HDMI should be specified separately. As for the versions, the following options are relevant today:

— v 1.4. Relatively old (2009), but still quite widely used version. Supports resolutions up to 4096x2160 (at 24 fps), as well as frame rates up to 120 Hz, which allows you to play 3D content as well. It is found both in the original version and in improved versions v 1.4a and v 1.4b — they have advanced features for working with 3D.

-v 2.0. Version released in 2013. The increased bandwidth compared to its predecessor made it possible to provide full support for 4K video (at frame...rates up to 60 Hz), as well as multi-channel audio up to 32 channels and 4 streams over a single cable. HDMI v 2.0 did not originally support HDR, however this feature was introduced in the v 2.0a update and was improved and expanded in v 2.0b. With all this, old cables, originally designed for version 1.4, are also suitable for connecting according to this standard.

— v 2.1. Standard introduced in 2017. Also known as HDMI Ultra High Speed, bandwidth has increased so much that it is possible to transmit video at resolutions up to 10K at 120 frames per second. Note that to use all the features of this version, you need cables that were originally created for it (although the functionality of earlier versions will be available when connected via a regular cable).

In conclusion, we note that different versions of HDMI are mutually compatible, however, the signal transmission capabilities in such cases will be limited by the characteristics of the older and slower standard.

A digital connector originally designed for video transmission, but more recently also supports audio. Technically, it is in many ways similar to the HDMI described above, but it has a narrower specialization, it is mainly used in computer technology to connect monitors. Through a monitor connected directly to the NAS server, you can monitor the operation parameters of the device; and some DisplayPort models also allow keyboards and mice to be connected for direct server control. In some cases, this format of work is more convenient than access via the network.

Output for audio transmission (including multi-channel) in digital form via optical cable. It is found mainly among NAS servers positioned as network media centers: such devices can directly broadcast sound via S / P-DIF to an external audio device (active speakers, amplifier, etc.). At the same time, the server can be supplemented with special tools for working with sound, for example, support for network radio stations or streaming audio services.

The optical connection is remarkable in that it is not afraid of electrical interference, but the cable itself is quite fragile and requires careful handling.

The presence of at least one USB connector on the front panel of the NAS server. This connector can comply with different standards, most often it is USB 3.2 gen1, less often USB 2.0 or USB-C. For more information about these standards, see above, here we recall that USB ports allow you to connect various peripherals — primarily storage drives for data exchange (or extensions working capacity of the server), and sometimes also keyboard/mouse for direct control. In addition, these ports can be used to charge various gadgets. And the location on the front panel provides the fastest and easiest access to the connectors.

— Web server. Ability to use the device as a Web server. It is on servers of this type that the Internet in its current form is built: the user's computer sends a request to a web server through a browser and receives a response in the form of a page, picture, video / audio stream, etc. Accordingly, the presence of this function in the NAS allows you to view its contents in the form of web pages using a regular browser — roughly speaking, "walk through the server, like on the Internet." In this case, the device can be used not only as a local resource, but also as a web host — for example, host the company's official website on it.

— FTP server. FTP is an abbreviation for File Transfer Protocol, i.e. file transfer protocol. This feature allows you to use the NAS server as a shared data storage: users can "upload" their own files to storage and download them from there. FTP tools provide ample features for configuring access to server content — for example, you can set restrictions on writing information to individual users or to individual folders, close part of the content with passwords, etc. Due to this, this protocol is much more convenient for working with individual files than the HTTP used in web servers (see above). Therefore, if you plan to create shared storage on the network, it is advisable to have a NAS with FTP server function.

— Print server. The print server feature makes it easy to share the same printer among network users. The printer is connected to the NAS, usually via a USB interface (see above), and the NAS serves as an intermediate link: it receives print jobs from users and sends them to the printer. Additional print server features can include sequencing optimization, local job storage (document will be printed even if you turn off the computer from which the job was sent), deletion of "overdue" jobs, and even accounting for the number of pages and remaining consumables. Using a NAS with a print server function is often more convenient than connecting a printer through one of the regular computers on the network.

— Multimedia (DLNA, iTunes, uPnP).... NAS server supports various functions related to the exchange of multimedia content. For example, DLNA (Digital Living Network Alliance) is a standard, one of the functions of which is the general access of various network devices to video, audio and photos stored on a local network; while streaming is also supported. The iTunes player has multimedia networking features similar to DLNA, but was created specifically for Apple electronics and is used primarily in it. uPnP (Universal Plug and Play) is a technology that facilitates the automatic configuration of local networks, including to share content. A server with multimedia functions should be looked for in the first place if the ability to work with streaming video / audio is important for your local network.

— Transcoding. A function that allows you to convert audio and video materials from one format to another directly during playback. In other words, the file on the NAS server is stored in one format, and it can be sent to an external device in another, the server itself will provide the conversion. It should be taken into account that the set of supported formats and general transcoding capabilities may be different (in particular, the maximum video resolution is inevitably limited); these nuances should be clarified in each case separately. However, this function anyway significantly expands the possibilities for playing multimedia content and reduces the likelihood of compatibility problems.

— BitTorrent client. The presence in the device of its own torrent client or other data exchange protocol (HTTP, FTP, etc.). This feature allows you to work with file-sharing networks, which are built on the principle of "everyone's own server": the downloaded information is not on a separate computer on the network, but on the computers of the same users. At the same time, the same file can be opened for download in several places and the torrent client simultaneously downloads different parts of it from different sources - this significantly increases the speed. Using a torrent client on a device is convenient in two ways. Firstly, it allows you to offload the main computers of users - an important advantage, given that the torrent client can consume a lot of resources, especially with an abundance of simultaneous downloads / distributions. Secondly, network equipment tends to stay on at all times, allowing downloads and uploads to continue even when users' PCs and laptops are turned off. However, it should be taken into account that despite the presence of such functionality in devices, the open placement of content in torrent networks can violate copyrights. Therefore, use torrent clients in compliance with legal regulations.

— Mail server. Ability to operate the NAS in server mode for e-mail processing. On such a server, you can create mailboxes in the format [user]@[company_name].com, it works as a storage for incoming letters and as a forwarding service for outgoing ones. Additional features may include automatic redirects, spam protection, custom filters, and so on. Having this feature is indispensable if you need a corporate email system: your own internal storage is more reliable in terms of security than external email services, and the ability to create unique email addresses can also come in handy.

— Database server. As the name implies, this function is useful for creating databases — systematized arrays of information designed to be accessed and processed from a computer. It is usually implemented through support for the SQL language. Its peculiarity lies in the fact that the network user does not need to know the specific location of the information in the database — it is enough to issue a request, what kind of data needs to be obtained, and the server itself searches for it. This is very convenient when working with large volumes of information, while high power is not required from user computers — the main load falls on the server.

— Surveillance server. A set of software tools that allow you to use the NAS as a storage for video recordings from surveillance cameras. Features of video storage may be different. For example, in some servers, a certain part of the working volume of drives can be allocated for this, and when it overflows, the oldest records are automatically deleted, freeing up space; in others, deletion is carried out not by volume, but by date — for example, materials are stored for a month, then deleted. Both the volume and the shelf life, usually, can be set by the user himself. And some models with a VGA output (see above) can also be used as live surveillance systems — the image from the cameras is displayed on the monitor in real time, which can be useful, for example, for organizing security. The specific features of the operation of the NAS in the video server mode may vary from model to model, this point is best specified according to the manufacturer's official data.

— Backup. The backup function is designed to create a backup copy of data (so-called backup) in case of loss or damage to information on the primary media. Backup can be done to the built-in or external drive, and even to another device over the network. To facilitate this task, many developers create various specialized software tools; in this case, it is assumed that the NAS server supports one of these tools. Also, software capabilities can be supplemented by hardware ones — for example, a separate quick copy button.

– ZFS file system. An advanced file system that uses a transactional copy-on-write model. Active data is never overwritten - ZFS places the new block in a different location on disk and updates the metadata, which allows you to write a link to the new block of information and save older versions of the data. The key features of ZFS are snapshots (immutable copies of the file system made on the fly), advanced compression algorithms, and a built-in deduplication function. ZFS is also one of the most advanced file systems in terms of security.

— DDNS. Short for Dynamic DNS — "dynamic DNS". This feature allows you to assign a permanent domain name to a device with a dynamic IP address. A domain name is the name of a device on the local network or the address of a site on the Internet (for example, m.ua or e-katalog.ru). An IP address is service information in the form of a digital code; it is thanks to her that network equipment can find the desired device and issue the required data from it. Actually, IP is the primary network "coordinates"; however, remembering addresses as a sequence of numbers is quite difficult, so domain names appeared — they are much more convenient for a person. Both on the Internet and in local networks, the connection between a domain name and an IP address is responsible for the so-called DNS servers: for each domain in the database of such a server, its own IP is registered. However, for technical reasons, there are often situations where the NAS server has to use a dynamic (changing) IP; accordingly, in order for information to be constantly available on the same domain name, it is necessary to update the data on the DNS server with each IP change. It is this update that the DDNS function provides.

— Integration with. A software tool that makes it easy to integrate a NAS into an existing domain (computer network area). Each domain has a so-called a controller is a server that stores information about users, primarily logins, passwords, and access rights. When connecting a NAS with the integration function, all these settings can be automatically imported, so that all users have the same access rights to the contents of the NAS as to all contents of the domain. This saves the administrator the hassle of creating and configuring separate accounts (which can be quite a hassle on large networks).

— Airplay. NAS server support for AirPlay technology. This is an Apple proprietary development, originally created for wireless broadcasting of audio and video content from Apple technology to TVs, audio systems and other playback devices; however, nowadays, the role of the transmitter can also be performed by electronics from other manufacturers. This is what we are talking about in this case: AirPlay support allows you to broadcast video and/or audio content stored on the server from the NAS server to external devices. To do this, the NAS and the AirPlay-compatible signal receiver must be on the same network, and the signal receiver must be connected via Wi-Fi. Such a broadcast is usually controlled either through a browser on a computer, or through a proprietary application on a mobile device that plays the role of a remote control. Also note that, in addition to the original AirPlay, compatibility with AirPlay 2 can also be provided — this is an improved version of this technology, which introduced, in particular, the ability to work in the multiroom format (simultaneous broadcast of different audio tracks to different devices within the network).

— Chromecast. NAS server support for Chromecast technology. This technology, developed by Google, is in many ways similar to the AirPlay described above: it is intended primarily for broadcasting audio and video to playback devices wirelessly. Accordingly, the use of Chromecast is almost the same: a NAS server with this function can broadcast the content stored on it to a TV, projector, audio system, or other compatible playback device connected via Wi-Fi to the same local network. Management is also most often carried out through a web interface or using a mobile application.

The operating system (OS) installed on the NAS server as standard. The OS is the software basis for the functioning of any computer; it is impossible to use the machine without it. Accordingly, when purchasing a server with a pre-installed OS, you get a practically ready-to-use device — additional steps, in fact, come down to fine-tuning the system and installing (if necessary) additional software.

Various specialized applications are available for different operating systems to facilitate the use of NAS server functions; some of them (see "Programme Features") may also be preinstalled. Accordingly, knowing the name of the OS, it is possible, to a certain extent, to determine the tools available for working with the device.

Note that some operating systems are paid, and their cost is included in the price of the NAS.

The model and specifications of the processor installed in the NAS server. The speed of the device largely depends on these characteristics, primarily the clock frequency. However, in fact, this parameter is often more of a reference value: simple everyday tasks (say, FTP and print servers, see "Software Features") do not require high computing power. But for working with extensive databases (see ibid.), a “faster” processor may be useful.

The number of cores provided in the processor of the NAS server.

Initially, each core is a computing module designed to execute one sequence of instructions. Accordingly, multiple cores make it possible to work simultaneously with multiple data streams, which improves flow Rate - especially when processing multiple tasks at the same time. Also, in modern CPUs, multithreading technologies are increasingly being used, which allow loading each core with two sequences of commands at once. During the inevitable pauses in the execution of one of the threads, the kernel does not idle, but works with another sequence. As a result, the total number of threads in such processors is twice the number of cores; this scheme of work even more noticeably improves flow Rate.

It is also worth remembering that the overall capabilities of the processor are highly dependent on a number of other characteristics - microarchitecture, clock speed, support for special functions, etc. This means that a large number of cores does not in itself guarantee high flow Rate: for example, an inexpensive mobile processor on 4 cores may well be "weaker" than an advanced desktop chip with only 2 cores. However, if we are talking about a CPU with a similar specialization and clock speed, then a solution with a large number of cores ( 6 cores, 8 cores, or ev...en more) and multithreading support usually turns out to be more productive.

Clock speed of the processor installed in the NAS server.

The clock frequency is the frequency of the built-in oscillator, according to which all operations performed by the processor are synchronized. The higher this frequency, the more operations per second the CPU can perform and the easier it is to provide high computing power in it. However, note that the actual speed of the processor depends on many other features — the number of cores (see above), microarchitecture, volumes of the built-in cache memory, etc. So, only chips with similar characteristics and purpose can be directly compared by clock frequency ( desktop/mobile) and price category.

Processor clock speed achieved in TurboBoost or TurboCore "overclocking" mode.

Turbo Boost and Turbo Core technologies are used by different manufacturers (Intel and AMD, respectively), but they have the same principle of operation: load distribution from more loaded processor cores to less loaded ones to improve performance. The "overclocking" mode is characterized by an increased clock frequency, and it is indicated in this case.

For more information about clock speed in general, see the relevant paragraph above.

The amount of RAM on the NAS server. Along with the processor, it is one of the indicators that determine the speed of the system — the more memory, the higher the computing power. However, in fact, it does not always make sense to chase large amounts of "RAM", which can reach 4 GB, 8 GB and even higher; see "Processor" for details.

The maximum amount of RAM that can be installed on the NAS server. It depends, in particular, on the type of memory modules used, as well as on the number of slots for them.

The total number of slots for RAM modules provided in the device; in fact — the maximum number of slats that can be installed simultaneously in this model.

Features for upgrading RAM directly depend on this indicator. So, in low-cost models, there is often only 1 slot, and the only upgrade option is to replace the “native” bar. In more advanced devices, two or even four slots may be provided, while some of them may be free in the initial configuration.

The amount of native built-in memory provided by the NAS server.

This memory is mainly used to store the operating system that controls the server, as well as some service data. Its quantity is chosen in such a way that it is guaranteed to be enough for the normal operation of the main functions of the server. Therefore, most often this indicator has a purely reference value; it makes sense to pay attention to it if you choose a model with extensive additional functionality and the ability to install third-party applications. In such solutions, the volume of the built-in storage can already be measured in gigabytes, while in simpler devices it is hundreds or even tens of megabytes.

How to access NAS server management.

— Web interface. With this control, access to the settings is carried out through a regular browser: by connecting the NAS to a computer network, the user enters a special service address specified in the device documentation and gets to a web page through which control is carried out. One of the key advantages of this option is the ability to control it from any computer on the network, or even remotely via the Internet: it is enough to know the address and login / password. Due to simplicity and convenience, the vast majority of modern NAS servers are managed through a web interface.

— Utility. Server management through a special service programme (utility) installed on the host computer. This option is considered obsolete and is very rare. The main reason is the inconvenience compared to the web interface (see above): you need to spend time installing and configuring the utility, while the browser on most modern PCs is available by default.

The amount of power consumed by the NAS server during normal operation. Most often, we are talking about maximum power consumption — with all the occupied slots for drives, under high load.

Modern NAS, even high-performance ones, have rather modest power consumption — even among professional models with 10 or more drives, this figure rarely exceeds 1 kW. So there are no problems with connecting to a 230 V network. However, energy consumption information can be useful for some special applications, primarily for estimating the load on UPSs, emergency generators, stabilizers, and other special equipment.

The presence of its own display in the design of the NAS server. Usually this is the simplest liquid crystal matrix designed to display various service information: drive status, data on free / occupied space, messages about special operating modes or failures, etc. This equipment allows you to get data about the server without using a computer or an external monitor; on the other hand, such a need rarely arises, and the data on the PC / monitor still turns out to be more detailed. Therefore, there are few models with a display nowadays.

A remote control is included with the NAS server.

When using the device for its main purpose, as a server itself, the remote control is not required. Therefore, this function is found only in models with advanced multimedia capabilities — DLNA, iTunes, video surveillance server, etc. (see "Software Features") — as well as at least one video output, most often HDMI (see above). The convenience of the remote control is obvious: it allows you to give commands (for example, to control the built-in player), without approaching the device for this.

The type of cooling used in the NAS server.

— Active. Active cooling systems work on the principle of a heat pump — they forcibly remove heat from heating parts. In computer technology, including NAS, this function is usually performed by coolers — combinations of fans and heatsinks. Active cooling requires its own power, takes up a relatively large amount of space, and increases overall power consumption; in addition, it creates additional noise during operation, and it affects the cost. However, all these shortcomings are compensated by high efficiency: systems of this type can be used even in professional high-performance servers. As a result, they have become widespread.

— Passive. Cooling based on the natural removal of heat from heating elements; in other words, such systems do not take heat forcibly, but only facilitate cooling. The most common type of passive cooling in computer technology is a radiator — a ribbed metal plate; its action is based on increasing the area of contact with air. Sometimes radiators can be supplemented with so-called heat pipes that work by evaporating and condensing liquids. All types of passive cooling have simplicity, low cost and almost complete absence of noise during operation. At the same time, their efficiency is very low, and it makes sense to use such systems only in relatively simple low-power NAS servers.

The noise level produced by the device during operation. These data will be useful, first of all, to those who are trying to reduce the noise level as much as possible and, as they say, “fight for every decibel”. However, it is worth noting here that manufacturers can cheat and indicate the noise level for different modes.