Comparison QNAP TS-253Be RAM 4 GB vs QNAP TS-253B RAM 4 GB

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.

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 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).

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.

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.