I actually have 4 SATA 3.0 disks on my home server and I want to organize them in order to have the best performance on my 10 RAID ZFS array

  • Seagate ST2000DL003 - Capacity : 2TB, Bandwith : 6GB/s, Cache : 64Mo, 5900 RPM, 4K physical sector
  • Seagate ST2000VN000 - Capacity : 2TB, Bandwith : 6GB/s, Cache : 64Mo, 5900 RPM, 4K physical sector
  • 2x Hitachi HUA723020ALA640 - Capacity : 2TB, Bandwith : 6GB/s, Cache : 64Mo, 7200 RPM, 512B physical sector

Should I put the Seagate's and Hitachi's drives together or should I make two Seagate/Hitachi mirrored array for having the best performance ?

  • Are you optimizing for best read performance or best write performance? Are you optimizing for sequential access or random access? – kasperd Apr 10 '17 at 22:54

It is not generally recommended to mix 5900 and 7200 RPM disks in the same array. Anyway, I suggest you to match the same disks in each mirror. In short: make a mirror of the 5900 RPM devices + another mirror of the 7200 RPM devices, then stripe them together.

The most important thing to do is, anyway, to align the ZFS vdev/filesystem to a 4KB boundary, via the ashift=12 option.

  • Should I set ashift=12 to both mirrored vdevs ? Or just for the 4k drive and ashift=9 to the other ? – Benjamin CHAINTREUIL Apr 9 '17 at 15:25
  • If I remember correctly, ashift is a global parameter, rather than vdev-specific. Anyway, I would set it for the entire array. – shodanshok Apr 9 '17 at 18:38
  • ashift is disk-specific, at least on illumos, see for example wiki.illumos.org/display/illumos/… I would even argue that this is the only configuration that makes sense so that you can mix and match older and newer disks. – user121391 Apr 10 '17 at 7:11
  • ashift is disk-specific also on ZFS on Linux. This can be configured through zdb if you are so inclined. – a CVn Apr 24 '17 at 11:42

Ideally, you would use equally-sized and equally-spec'd disks in your array if you're concerned about performance or consistent operation.

Is there a reason you can't use the same type of drive?

  • My disks are already equally sized... I talk about other factor like sector size, and speed of rotation – Benjamin CHAINTREUIL Apr 9 '17 at 14:06
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    They may be equally sized, but they spin at very different speeds. Scheduling writes to these disks in an array is going to be troublesome, and we're going to be waiting on the 5400 RPM drives often enough to cause performance troubles. – Spooler Apr 9 '17 at 18:16

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