The hard drive market undergoes regular changes that often go unnoticed by consumers. However, it is simply impossible not to notice some changes.
Today, manufacturers of hard drives produce two main formats of hard drives - with a form factor of 3.5" and 2.5" inches.
Often, instead of specifying the specific form factor of a hard drive in inches (and the double quotation marks indicate the inch itself), computer hardware vendors use the abbreviations SFF and LFF, short for Small Form Factor and Large Form Factor, respectively. Thus, smaller 2.5" form factor hard drives are labeled SFF, while 3.5" are labeled LFF.
It's no secret that in modern high-performance hard drives of 3.5" and 2.5" form factors, manufacturers use plates of the same size - from 2.5" HDD. Therefore, most often, both the capacity and performance parameters of 2.5" and 3.5" models of hard drives from the same manufacturer look the same What's more, some manufacturers have announced the cessation of production of high-performance hard drives in the 3.5" size, leaving only the top models in the 2.5" form factor. The availability of high-performance hard drives in the 3.5" form factor is steadily decreasing.
Based on the realities of the modern market, manufacturers consider it economically impractical to use more than 2 plates inside one hard disk. For reference, it is possible to install up to 3 plates in a 2.5" form factor hard disk (15mm high), and up to 5 plates in a 3.5" HDD.
What should those consumers who cannot or do not want (for various reasons) to use modern hard drives of the 2.5 form factor"?
Manufacturers offer an intermediate solution - the use of 2.5" hard drives in a 3.5" form factor. As a 3.5" hard disk, an ordinary 2.5" hard disk is offered, installed at the factory by the manufacturer in a special metal mounting case - a carriage. It should be noted that removing this hard drive from the mounting case is not compatible with the warranty of some manufacturers. Among the undoubted advantages of such a 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 the transition to the 2.5" form factor of hard drives give consumers?
It is obvious that the smaller the dimensions of the hard disk, the more such hard disks should fit inside the server.
Today, the following number of hard drives is traditionally installed in rack-mount servers:
As mentioned earlier, in the segment of enterprise-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 low price range, in which, today, the maximum capacity of 3.5" form factor hard disks is about 2 times larger than that of 2.5" disks, the maximum capacity of disk subsystems with compartments of different form factors will be approximately the same (as can be seen from the table), it is possible to install 2 times more 2.5" form factor hard disks in servers compared to servers of the same size, but with 3.5" hard disks.
As an additional 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 occupies a smaller volume, which allows manufacturers to slightly reduce the dimensions of the 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" compartments in the server guarantees compatibility when installing SSD drives, and, what is especially relevant, in the future - during a possible modernization of the server.
Hard drives of smaller sizes are actively used in systems with small dimensions, in servers of high installation density, modular and blade servers.
Such a parameter 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) increases with the number of connected hard drives, so it is clear that more 2.5" drives will give a serious advantage compared to a small array with 3.5" HDDs.
For comparison, two 2.5" hard drives with 10,000rpm (revolutions per minute) of the corporate class on a good RAID controller will outperform one 3.5" drive with 15,000rpm. At the same time, the price of two 2.5" 10,000rpm disks with a volume of 300GB and one 3.5" 15,000rpm disk with a volume of 600GB will be approximately the same.
Such a parameter as the linear read/write speed on external tracks should, in theory, be higher in 3.5" hard drives than in 2.5" (at the same spindle rotation speed and at the same recording density), simply due to the physically larger size of the plates, but in reality, the differences are insignificant, because in high-performance hard drives of different form factors, plates of the same size are often placed.
In general, the more hard drives in a server, the greater the power consumption (the more powerful the power supply units should be), and the greater the heat generation (the more powerful the server's ventilation system and cooling costs should be). However, compared to 3.5" hard disk models, modern 2.5" hard disks have 2 times less power consumption (in all modes) and, as a result, less heat generation and cooling costs. Thus, a server with 24 2.5" hard disks consumes electricity and heats the surrounding space less than a server with 12 3.5" hard disks.
The reliability of hard drives is always given a lot of attention. Due to the reduction in dimensions (and additional engineering solutions), 2.5" hard drives have increased resistance to vibration and mechanical influences. This is confirmed by the manufacturers themselves, the MTBF in the latest models of 2.5" hard drives is 2 million hours, compared to the best models 3.5" hard drives, in which MTBF is declared at the level of 1.3-1.6 million hours.
And lastly, despite the fact that it is not relevant in servers, but 2.5" drives produce a little less noise during operation, compared to 3.5" models.
In conclusion, you can briefly formulate the pros and cons, as well as the areas of application of hard drives of various form factors.
Advantages of hard drives in different form factors
3.5" LFF - larger volume of one disk, lower price per gigabyte:
at the same recording density, more information is placed on a plate of a larger size
the maximum capacity of one HDD is larger (in the hard disk segment of the low price range)
cheaper cost per gigabyte of disk space
2.5" SFF - more capacity and performance per unit of space occupied by the server or storage system in the rack:
2 times more storage capacity in a limited space - smaller dimensions and, as a result, a higher density of capacity per unit of space volume (Gigabyte/cm.cube) or per unit of server size in the rack (Gigabyte/Unit)
higher performance of the storage system in limited space - smaller dimensions and, as a result, higher I/O density of the disk subsystem per unit of space volume (IOPS/cm.cubic) 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 influences, higher work-to-failure (MTBF)
less noise during operation
Fields of application of hard drives of various form factors
3.5" LFF:
in traditional servers and data storage systems, in which the size (the dimensions of the server body) is not a determining factor - general purpose servers
in servers or large-capacity data storage systems that do not require high performance - 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 mounting servers, modular and blade servers
in systems with high performance of the disk subsystem due to a large number of fast hard disks - 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 energy consumption - hosting servers, data center
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