Recently got a dell T320 with a percH310 controller, and I've decided to put the OS on a raid 5 of 3x300GB 15k SAS drives but would like a hot spare, we have a spare 15k 300GB sas drive which has been a hot spare in the old server, and has never been used it's from 2013. My priority here is placed on redundancy and reliability/uptime over performance.

1) Will this have any detrimental/negative effects such as reduce reliability of automatic raid rebuilds, load other disks higher when in use, or any such?

2) Would i be better off setting all 4 up in a raid 10 array or again could this older drive cause me any potentially dangerous circumstances or even just reduce performance of the other drives?

This won't be containing most of the data this will be on a separate SATA raid 10 of 6TB drives.

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    Make sure that the disk has equal or larger size than other disks in the array! 300GB may not be the same 300GB... – Jaroslav Kucera Nov 14 '17 at 14:14

Regarding detrimental effects in a RAID5 specific to the drive being older:

  • Test the drive as a non-spare drive first (perhaps as a single-drive RAID0) and verify that it doesn't fail under workload. Try a tool that allows you to read/write the full capacity of the drive so you don't get hit by existing undiscovered bad sectors later on.
  • Make sure the older drive is running up to date firmware.
  • Note comment from Jaroslav Kucera. If the old drive is a few sectors smaller, it may not be able to support the others as a spare. You could probably avert this by making your virtual disk 1GB smaller than the full space available.

If your priority is on "redundancy and reliability/uptime over performance", RAID10 is absolutely a better choice. RAID5 is technically still acceptable by industry standards for that drive capacity/speed, but RAID10 will be safer by far. You should consider testing the drive as mentioned above (test under load, update firmware, etc).

Another option to consider, again in the name of redundancy and reliability/uptime over performance, would be RAID6. The H310 does actually support RAID6 on four spindles. You would see the same usable capacity as you would with RAID10, with the added benefit that ANY two drives could fail without losing data access. This also prevents stripe punctures after a single drive failure and rebuild, which you might run into with RAID10 if the non-failed drive in a mirror has new bad blocks encountered during rebuild.

  • If your priority is on "redundancy and reliability/uptime over performance", RAID10 is absolutely a better choice. To me, that seems to say that RAID5 would outperform RAID10. RAID10 almost certainly will outperform RAID5, giving it better reliability/uptime and performance. The real choice would be between the performance of RAID10 and slightly better availability of RAID6. – Andrew Henle Nov 15 '17 at 11:44
  • Thanks for the precise answer, so if i were to update the fw on the device, and test with HDTune and both report it's fine, putting this in a raid 10 is going to perform like any normal SAS? My doubts came from the fact we have had SATA 2 and 3 during this drive's life, and i wasn't sure if there was similar differences in terms of SAS? – user3407675 Nov 15 '17 at 12:46
  • @AndrewHenle It was intended as a comparison between "keeping the potentially untrustworthy 4th drive as a spare for RAID5" and "using the 4th drive actively in a RAID10", but you're absolutely right. RAID5 would be inferior in every way unless comparing all four drives active, giving RAID5 a small capacity advantage (and much greater risk to data). – JimNim Nov 15 '17 at 21:32
  • @user3407675 That's a great point - I did not consider the possibility of different interface generations. You probably ought to test the old drive AND one or more of the new ones to verify there's no major difference in performance capability. – JimNim Nov 15 '17 at 21:35
  • @JimNim how would you suggest i best go about conducting this test? And if they are different interface versions, will it just cause a speed issue or potentially a stability issue as well? Thanks again for your advice here :) – user3407675 Nov 16 '17 at 15:36

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