Consumer (or prosumer) SSD's vs. fast HDD in a server environment

Solution 1:

Note: This answer is specific to the server components described in the OP's comment.

  • Compatibility is going to dictate everything here.
  • Dell PERC array controllers are LSI devices. So anything that works on an LSI controller should be okay.
  • Your ability to monitor the health of your RAID array is paramount. Since this is Dell, ensure you have the appropriate agents, alarms and monitoring in place to report on errors from your PERC controller.
  • Don't use RAID5. We don't do that anymore in the sysadmin world.
  • Keep a cold spare handy.
  • You don't necessarily have to go to a consumer disk. There are enterprise SSD drives available at all price points. I urge people to buy SAS SSDs instead of SATA wherever possible.
  • In addition, you can probably find better pricing on the officially supported equipment as well (nobody pays retail).
  • Don't listen to voodoo about rotating SSD drives out to try to outsmart the RAID controller or its wear-leveling algorithms. The use case you've described won't have a significant impact on the life of the disks.

Also see: Are SSD drives as reliable as mechanical drives (2013)?

Solution 2:

Yes, the SSDs will be way faster than the SAS drives. For sequential throughput, a good RAID of SAS drives might do pretty well, but for random access, the SSDs will blow them out of the water which can result in a very noticeable performance difference.

Depending on the particular SAS drives and the particular SSD drives, the SSDs may have a better unrecoverable read error rate by up to a factor of 10.

Some tips for if you do use consumer SSD drives:

  • Know your write workload so you can estimate how often you'll have to replace the drives since they have a certain amount of write endurance
  • If you can spare the space, overprovision the drives to make them more like enterprise ones
  • Check out articles comparing the performance and write endurance characteristics of SSDs in the the same class and pick the one best suited to your needs
  • Personally I'd get SSDs with a 5 year warranty because I believe the manufacturer is going to provide better quality as a result. I know this isn't a hard and fast rule, just personal belief.
  • There are low end consumer SSD drives and higher end one - sometimes labeled something like "Pro" - you might want to look for ones in that class
  • This goes for enterprise drives too, but be sure you're monitoring the MWI (media wear indicator) so you know when to replace the drives

Solution 3:

Consumer grade SSDs will work fine in many servers for use cases.

They are way, way faster then SAS disks. I'd suggest the reason to get enterprise disks over consumer disks is not the speed, its the read-write cycles and better engineering - for example supercaps are present in some enterprise SSD's where the consumer grade version does not have this - if you loose power to the server your data is less likely to be killed.

You need to be aware that RAID is not backup - if you are going to RAID a couple of SSD's thats fine, but get different brands of SSD's, or at least different models so they have different performance characteristics. WHEN SSD'S DIE THEY ARE WAY MORE LIKELY TO DO SO WITHOUT WARNING, AND NO ABILITY TO PULL DATA OFF - on the flip side they are 10x as reliable as regular hard disks.

Look into the Samsung 850 series disks - at least for 1/2 the array - they are/were prosumer and offer good bang for buck, and are touted as being more reliable then 2d nand. (They use 3d nand).

Also, as someone else mentioned, don't do RAID5. Drives hold to much for it to work reliably - and back up your data.

Solution 4:

If you are using them for writes, to avoid data corruption in the event of power failure you need to make sure that you only consider models with a supercap. Eg. Intel S3500, Samsung 845DC Pro

Otherwise consumer SSDs are more suited to caching.

Solution 5:

Even consumer-grade SSDs are much faster than the faster 15k HDDs, so from a performance standpoint they will be fine (if using the right disk and if overprovisioning them), but you had to carefully pick them, especially due to how they interact with hardware-based RAID controller...

  1. First, check if affordable, entry-level enterprise grade drive (as Intel S3500/S3600, Micron M500DC and Micron M510DC) are within your reach. If so, you can skip the whole consumer-grade lottery.
  2. Check whether your RAID cards support 3rd party disks. For example, earlier DELL firmware for H700/H710/H710p cards refused to initialize non DELL-rebranded disks. A subsequent update initialized such disks, but marked the array "degraded". Only relatively recent (end 2013) firmware updates corrected that precarious situation.
  3. Keep your disk's private cache enabled. Some RAID card will forcibidy disable the disk's private cache. This kill performance for consumer-level SSD, as they make heavy use of private DRAM cache both to cache their indirection table and to mask the heavy latency involved into erasing/programming MLC NAND. For example, an otherwise very fast Crucial M550 240GB drive write at incredibly slow rate of 5 MB/S when its internal cache is disabled.
  4. If possible, strongly favor disks with FULL power-loss protection. This put squarely in the enterprise champ but, as stated above, there are relatively cheap disks in this champ.
  5. If no full power-loss protected SSD are in your shop list, at least use disk with partial power-loss for data-at-rest protection. Some excellent driver with such protection are the Crucial/Micron M500/M550 and the newer M600. Micron even has an interesting document on how/why overprovision its M600 drive for use in virtualization environment. Anyway, remember that with non-full power loss protected drives, it remain a small possibility to lose/corrupt your data. How small? it depends on your RAID controller behavior (for example, if it issues a final ATA flush command after transferring data to a cache-enabled disk) and on the disk's firmware, so it is not possible to give you a detailed answer. What I can say is that on all my tests, PERC RAID cards seems to always flush the disk's private cache (if it is enabled)
  6. Strongly over-provision your consumer drives, at least with a 25/30 % reserved capacity.
  7. Do not use second-class consumer drives. Even good consumer drivers have their problems, and going with a lower-tier consumer disk is asking for troubles.