For a few years we have been ignoring a completely new class of hard disk drives – server disks of the 2.5-inch form-factor. It’s time to improve the situation now.
First of all, let’s recall why this product class was invented. Quite a long time ago, when we were all much younger and the recording density was much lower, when SSDs were not even heard of and CPUs had legs, some clever engineer must have recalled the famous maxim that God is always on the side of the large battalions. So, that engineer came up with an idea of how to improve a disk subsystem performance by means of adding more disks into it. The idea is quite simple and, judging by our reviews of RAID controllers, effective. If the controller is capable enough, the performance of the disk subsystem scales up well depending on the number of disks. However, a standard HDD rack can only accommodate a limited amount of disks even when you want to add more and more to boost your disk performance even higher. The solution is as simple as the RAID concept itself: the physical size of a hard disk drive must be reduced!
Indeed, if our priority is the number of input-output operations per second rather than the storage capacity, it makes sense to replace physically larger HDDs with smaller ones. For example, you can install six 2.5-inch drives into a 1U server instead of four 3.5-inch ones – an advantage of two spindles! The only question is whether the smaller HDDs have high speed characteristics. Of course, they are going to have lower sequential speeds, but what about the number of disk operations per second?