The hard drive market is constantly changing, often unnoticed by consumers. However, some changes are simply impossible to ignore.
Today, hard drive manufacturers produce two main hard drive formats - with a 3.5" and 2.5" form factor.
Often, instead of specifying the specific form factor of a hard drive in inches (and the double quote denotes an inch), computer equipment suppliers use the abbreviations SFF and LFF, short for the phrases Small Form Factor and Large Form Factor, respectively. Thus, hard drives of a smaller form factor of 2.5" are designated SFF, while 3.5'' are designated as LFF.
It's no secret that in modern high-performance hard drives of 3.5" and 2.5" form factors, manufacturers use platters of the same size - from 2.5" HDD. Therefore, most often, both the capacity and performance parameters of 2.5" and 3.5" hard drive models from the same manufacturer look the same. Moreover, some manufacturers have announced the cessation of production of high-performance 3.5" hard drives, leaving top HDD models only in the 2.5" form factor. The availability of high-performance 3.5" hard drives is steadily decreasing.
Based on the realities of the modern market, manufacturers consider it economically impractical to use more than 2 platters inside one hard drive. For reference, up to 3 platters can be installed in a 2.5" form factor hard drive (15mm high), and up to 5 platters in a 3.5" HDD.
What should consumers do who cannot or do not want (for various reasons) to use modern 2.5" form factor hard drives?
Manufacturers offer an intermediate solution - the use of 2.5" hard drives in the 3.5" form factor. As a 3.5" hard drive, a regular 2.5" hard drive is offered, installed at the factory by the manufacturer in a special metal mounting housing - a carriage. It should be noted that removing this hard drive from the mounting housing is incompatible with the warranty for some manufacturers. Among the undoubted advantages of this design, it should be noted that the engineers of the manufacturing companies accurately calculate the dimensions and rigidity of the structure, guarantee the standard arrangement of connectors and mounting holes for 3.5" hard drives, and ensure optimal cooling of the hard drive installed inside.
If the transition to a smaller form factor is inevitable, what will consumers gain from switching to the 2.5" hard drive form factor?
Obviously, the smaller the hard drive, the more such hard drives must fit inside the server.
Today, rack-mount servers traditionally have the following number of hard drives installed:
As mentioned earlier, in the segment of corporate-class hard drives, the maximum capacity of drives of two different form factors is the same, based on this, the use of a disk subsystem with 2.5" bays allows you to double the maximum total storage capacity. And even in the case of using hard drives of a low price range, in which, today, the maximum volume of 3.5" form factor hard drives is approximately 2 times larger than that of 2.5" drives, the maximum capacity of disk subsystems with bays of different form factors will be approximately the same. In the general case (as can be seen from the table), it is possible to install 2 times more 2.5" form factor hard drives in servers, compared to servers of the same size, but with 3.5" hard drives.
As an added bonus of using 2.5" hard drives, it is obvious that due to the smaller dimensions (a 2.5" drive is smaller than a 3.5" drive in depth), the disk subsystem in the server takes up less space, which allows manufacturers to slightly reduce the size of servers. It should also be noted that most modern SSDs (solid-state drives) are produced in the 2.5" form factor, and the use of 2.5" bays in the server guarantees compatibility when installing SSDs, and, what is especially important, in the future - during a possible server upgrade.
Smaller hard drives are actively used in small-sized systems, high-density servers, modular and blade servers.
A parameter such as the maximum amount of disk space is, of course, important, but not always. In enterprise-class server disk subsystems, the performance of the disk subsystem (the number of input/output operations per second, IOPS) is much more important than the total capacity of the disk storage.
The number of RAID groups (LUNs) of the disk subsystem and their performance (IOPS) increase with the number of connected hard drives, so it is obvious that a larger number of 2.5" drives will give a serious advantage compared to a small array of 3.5" HDDs.
For comparison, two 2.5" 10,000rpm (revolutions per minute) enterprise-class hard drives on a good RAID controller will outperform one 3.5" 15,000rpm drive. At the same time, the price of two 2.5" 10,000rpm drives with a capacity of 300GB and one 3.5" 15,000rpm drive with a capacity of 600GB will be approximately the same.
A parameter such as the linear read/write speed on external tracks should theoretically be higher in 3.5" hard drives than in 2.5" (at the same spindle speed and recording density), simply due to the physically larger size of the platters, but in reality the differences are insignificant, because high-performance hard drives of different form factors most often have platters of the same size.
In general, the more hard drives in a server, the greater the power consumption (the more powerful the power supplies must be) and the greater the heat dissipation (the more powerful the server ventilation system and cooling costs must be). However, compared to 3.5" hard drive models, modern 2.5" hard drives have 2 times less power consumption (in all modes) and, as a result, less heat dissipation and cooling costs. Thus, a server with 24 2.5" hard drives consumes less electricity and heats the surrounding space than a server with 12 3.5" hard drives.
Hard drive reliability is always given great attention. Due to the reduced dimensions (and additional engineering solutions), 2.5" hard drives have increased resistance to vibration and mechanical stress. This is confirmed by the manufacturers themselves, the mean time between failure (MTBF) of the latest 2.5" hard drive models is 2 million hours, compared to the best 3.5" hard drive models, in which the MTBF is declared at 1.3-1.6 million hours.
And finally, despite the fact that this is not relevant in servers, 2.5" drives produce slightly less noise during operation compared to 3.5" models.
In conclusion, we can briefly summarize the pros and cons, as well as the areas of application of hard drives of different form factors.
Advantages of hard drives in different form factors
3.5" LFF - larger capacity per disk, lower price per gigabyte:
at the same recording density, more information fits on a larger plate
the maximum capacity of one HDD is larger (in the low-price range hard drive segment)
cheaper cost per gigabyte of disk space
2.5" SFF - more capacity and performance per unit of space occupied by a server or rack storage system:
2 times more storage capacity in a limited space - smaller dimensions and, as a result, higher capacity density per unit of space volume (Gigabyte/cm3) or per unit of server size in a rack (Gigabyte/Unit)
higher performance of the storage system in a limited space - smaller dimensions and, as a result, higher input-output density of the disk subsystem per unit of space volume (IOPS/cm3) or per unit of server size in the rack (IOPS/Unit)
2 times less energy consumption (in all modes) and, as a result, less heat generation and cooling costs
increased resistance to vibration and mechanical stress, higher mean time between failures (MTBF)
less noise during operation
Areas of application of hard drives of different form factors
3.5" LFF:
in traditional servers and storage systems where size (server case dimensions) is not a determining factor - general-purpose servers
in servers or large-capacity storage systems where high performance is not required - file servers, archive or backup storage, NAS, video recording servers
2.5" SFF:
in systems where small dimensions are a determining factor - 1U rackmount servers
in high-density servers, modular and blade servers
in systems with high disk subsystem performance due to a large number of fast hard drives - application servers, operational databases
in systems with a large number of RAID groups - database servers
in systems with maximum reliability of all components - fault-tolerant servers
in systems with low or limited power consumption - hosting servers, data center
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