Comparison Ugreen CM400 vs Gembird EE2-U3S-6

The form factor of the drive that the pocket is designed to hold.

Such accessories are made for standard form factors of internal drives: 3.5 ", 2.5"(often — for both at once), as well as M.2 SSD. Here are the features of each of these options:

— HDD 3.5 ". 3.5" is the traditional form factor of internal drives for full-size desktop PCs. Accordingly, internal pockets for this form factor are used exclusively in PCs or servers, they are too bulky for laptops; moreover, most of these pockets are a chassis — "sled" (see "Purpose"). External solutions turn out to be more bulky than models under 2.5", however, due to the absence of strict restrictions on the size, capacious drives for such pockets are much cheaper than miniature analogues of the same capacity. Also note that most 3.5-inch drives are just traditional hard drives (or hybrid SSHD devices), SSD modules in this form factor are practically not produced.

SSD or HDD 2.5". Therefore, the internal pockets of this form factor are intended primarily for laptops; a classic version of such an accessory is an adapter for installing a drive in an optical drive slot. In PC models, this option has not received much distribution — modern desktops usually have not only 3.5-inch, but also 2.5-inch drive bays; and for a number of reasons, it is more convenient to use 3.5" solutions as quick-release "...sleds" (see above). But for servers, internal pockets of this form factor are available — for several slots; they usually also represent a "sled" chassis. What As for external models, 2.5" pockets are noticeably smaller than 3.5" counterparts, however, drives for them are more expensive per gigabyte of capacity (especially with large volumes).

— SSD or HDD 2.5"/3.5". Models designed for two form factors at once. The meaning of this marking depends on the particular type of pocket. So, in external models and docking stations (see "Type"), it usually means the ability to install a drive of any of the two form factors in your pocket, to choose from. Usually, bays or slots in such models are initially designed for 3.5", and special plugs are used to fix 2.5" drives in such slots (note that there may be fewer such plugs in docks than sockets). A similar design is used in internal models for servers, as well as in PC chassis that look like a "sled" (see "Intended use"). However, in PC models there is another option — adapters for accommodating 2.5" HDD / SSD in 3.5" form factor slots ; such accessories are also included in this category.

— SSD M.2. Form factor designed specifically for miniature internal components, including solid state drives. Dimensions of M.2 peripherals are from 12 to 30 mm wide and from 16 to 110 mm in length, such components are connected through the connector of the same name. External pockets of this form factor are compact in size. In turn, internal models are most often laptop solutions for installing an SSD in an optical drive slot. However, there is also a rather specific option — PC accessories that allow you to connect M.2 drives to a PCI-E slot (like a separate sound card or another expansion card).
Note that the connection via M.2 can be carried out both on the basis of PCI-E and on the basis of SATA; for more details, see "Drive interface", here we note that the current moment and compatibility with a specific drive should be specified separately.

Drive interface provided in the design of the pocket, in other words, a way to connect the drive.

It makes sense to use pockets for internal drives, so the appropriate interfaces are used for connection. Also note that in internal models (see "Type") the interface of the drive is often not specified, since it corresponds to the interface for connecting the pocket itself to the computer. As for specific options, here are the most relevant for today:

— SATA 3. The newest and most advanced, and in storage pockets, the most common version of the SATA interface. This interface is designed for internal storage, primarily hard drives; for SSD, it is relatively poorly suited, since it does not allow realizing all the potential of solid-state memory. Specifically, SATA 3 provides data transfer rates up to 600 MB / s, while earlier SATA drives can also be connected to such connectors — unless the connection speed is limited by the capabilities of a slower interface.
It is worth saying that in addition to traditional 2.5" and 3.5" SATA drives (see "Form factor") connected via the connector of the same name, nowadays you can also find M.2 form factor SSD modules that also use a SATA format connection . Such models are noticeably inferior in speed to solutions for M.2 PCI-E, but they are also cheaper. They are connected to the M.2 socket, which must support SATA.

— SATA 2. The predecessor of the SATA 3 described above; this version allows you to t...ransfer data at speeds up to 300 Mbps. In pockets, it is much less common, mainly among outdated models — for example, external solutions using USB 2.0 (see "Connection").

— PCI-E. A variant found exclusively on M.2 drive models (see Drive Form Factor). Such modules use the M.2 connector, the connection through which is most often implemented in the PCI-E format. At the same time, the specifications, usually, specify the version and number of PCI-E lines — the supported speeds directly depend on this. For example, the marking "PCI-E 3.0 2x" means 2 lines of PCI-E version 3.0; this version provides 984 Mbps per lane, so the overall speed is about 1.97 GB/s. However, nowadays, more advanced options are more common — for example, PCI-E 3.0 4x, where the speed is already about 3.9 Gbps. At the same time, drives and pockets with different versions and the number of PCI-E lanes in this case are usually compatible with each other, except that the speed will be limited by the capabilities of a slower interface.

— SATA/SAS. Models that support connection via two interfaces — SATA or SAS. The latter is a specialized standard used primarily in server systems; pockets with this feature also have a corresponding purpose. And this versatility is achieved due to the fact that SAS controllers are also compatible with SATA drives, so you can provide both types of connectors in your pocket. At the same time, SAS noticeably outperforms SATA in terms of operating speed — it is up to 22.5 Gbps, depending on the version (against a maximum of 6 Gbps in SATA). However, note that the SAS interface does not have a strictly defined type of connector — several types of plugs can be used for such a connection; this point needs to be specified separately.

The method of connecting a pocket with an installed drive to a computer, provided for in the design.

Note that this parameter is specified only in cases where the connection interface differs from the drive interface (see above). A similar feature is typical for all external models and docking stations (see "Type"): nowadays they most often use USB 3.2 gen1, less often — USB 2.0 or USB-C of one version or another (see below). In internal solutions, the drive connector rarely differs from the pocket connector, although there are exceptions.

It is also worth mentioning that in external models, the connection method is usually determined by the type of bundled cable; moreover, such a cable is often made removable, with the possibility of replacing it with a “cord” with a different type of plug.

As for specific connection methods, here are their main features:

— USB 2.0. USB is used to connect external peripherals, including pockets; this is the most popular modern interface of this purpose. And version 2.0 is the oldest USB standard in use today. The possibilities of such a connection are very limited — in particular, the power supply through the connector is 2.5 W, and the maximum data transfer rate does not exceed 480 Mbps. This is noticeably slower than even SATA 2 (3 Gbps), not to mention SATA 3 (6Gb/s); so in general this stan...dard is considered obsolete, and in pockets with this type of connection, the overall speed is limited just by the capabilities of USB 2.0. However, maintaining this interface is inexpensive; for simple tasks that are not associated with large volumes of information, it often turns out to be quite enough; in addition, USB 2.0 devices are fully compatible with newer USB ports. So nowadays you can still find pockets with this type of connection — these are basically the simplest and most inexpensive models.

— USB 3.2 gen1. Full size USB connector (not USB-C) compliant with version 3.2 gen1. This version (formerly known as USB 3.1 gen1 and USB 3.0) is the direct successor to USB 2.0, delivering up to 10x faster data transfer rates—up to 4.8Gbps—and more power. The mentioned speed is almost one-on-one with the capabilities of the popular SATA 3 internal interface; therefore, pockets with this type of connection are extremely common nowadays.

— USB-C 3.2 gen1. Connecting to a USB-C connector that complies with version 3.2 gen1. In terms of capabilities, this method is identical to the “normal” USB 3.2 gen1 described above, the difference lies only in the type of connector. USB-C is a relatively new standard used in both fixed and portable electronics. This connector is noticeably smaller than the standard USB A (slightly larger than microUSB), while it has a convenient double-sided design. However, specifically in computers and even laptops, USB-C ports are used much less frequently than full-sized USBs, so this option is relatively rare in pockets.

— USB C 3.2 gen2. Connecting to a USB-C connector that complies with version 3.2 gen2. See above for more details on USB-C in general. And USB 3.2 gen2 (formerly known as 3.1 gen2 or simply 3.1) is the successor to 3.2 gen1, with even more advanced features: the maximum connection speed in this standard is 10 Gbps. On the other hand, for SATA drives, such speed is unnecessary, support for this version is quite expensive, and USB-C 3.2 gen2 connection ports are still relatively rare. Therefore, this option has not received distribution in pockets either: it is provided only in individual models for M.2 SSD with PCI-E connection, where the speed of the internal interface is already measured in tens of gigabits per second.

— PCI-E. Connect to a standard PCI-E slot on the motherboard. In other words, such pockets are connected to the computer in the same way as video adapters, sound cards, and other expansion cards. This design is used in select internal models for M.2 SSD drives; using such a pocket, you can connect a similar drive to a desktop PC even if the native M.2 ports on the motherboard are busy, unavailable, not suitable for connection (for example, they use the SATA interface, while the drive is made for PCI-E), or absent altogether.
Note that such pockets are usually compatible with M.2 PCI-E SSD modules without problems, but compatibility with M.2 SATA should be specified separately (although such functionality is also found). It is also worth mentioning that PCI-E slots and devices for them can have a different number of lines, and the general rule here is this: the number of lines in a slot on the motherboard must be no less than that of the connected board. However, in pockets with such a connection, usually less than 4 lines are provided, so they can be connected to PCI-E connectors starting from 4x.

— IDE. Outdated interface for connecting internal drives. It is extremely rare in modern pockets — in separate models designed to install modern or HDD / SSD in outdated computers without SATA and other relevant connectors.

The maximum storage capacity supported by the pocket. In models with multiple disks/SSDs (see "Drive Slots"), this item indicates the largest total volume supported by the device; by dividing this capacity by the number of slots, you can determine the maximum allowable capacity of each individual drive.

The limitation on the maximum volume is relevant mainly for external models, including docking stations (see "Type"). This is due to the fact that fundamentally different interfaces are used for the drive and for connecting the pocket itself in such models (most often SATA and USB, respectively, see above for details). For the normal interaction of such interfaces, an electronic controller is required; and the larger the volume of the installed drive (s) — the higher the requirements for the performance of such a controller.

Note that, other things being equal, supporting large volumes is more expensive, and capacious drives themselves are not cheap. Therefore, when choosing according to this indicator, it is worth considering real needs, and not chasing the maximum numbers.