Raidz Question

[Mark]

Hi Guys,

I've been searching but struggling to find what I'm looking for. How is reliability 18 Disk RaidZ2 setup? The RAID Reliability Calculator only has RaidZ3. Right now I've got 2 x (6x2TB RaidZ2) with 14.6TB usable space. I was thinking about rebuilding and moving to 18 x 2TB in RaidZ2 to cut down on overhead. But I do realize I would be getting rid of parity drives and I don't want to expose myself to reliability issues. Any assistance would be greatly appreciated.

Thanks
-Mark

 

[neo]

Not speaking from personal testing, but I have always read you should not go over 6 disks for RAIDZ2

 

[markarr]

RAIDZ2 and RAID 6 offer the same level of parity. There are fundamental underlying differences but for parity calculations they are similar.

 

[Mark]

RAIDZ2 and RAID 6 offer the same level of parity. There are fundamental underlying differences but for parity calculations they are similar.

Thank you. Based on the calculator there is a very very small chance of failure for Raid 6. Yet if I move to RaidZ3 with 19 disk its showing 0%.

 

[mjt5282]

I wouldn't recommend changing your 2 raidz2 pools into 1 larger z3 pool - while it is reliable with larger disks (3Tb and beyond) the resilver times would be very long.

 

[Magnus919]

There are practical limitations to the number of pdevs in a zfs vdev depending on what RAID level you're going with. I don't know what that point of diminishing returns is with raidz2 vdevs but I'm pretty sure that 18 pdevs is past it.

 

[mjt5282]

There are practical limitations to the number of pdevs in a zfs vdev depending on what RAID level you're going with. I don't know what that point of diminishing returns is with raidz2 vdevs but I'm pretty sure that 18 pdevs is past it.

I run a media/mkv/flac server - i have a supermicro case with 16 drives - i was running a big raidz3 with 11 or 13 disks. I realized that the blu ray rips were taking up a large portion of the storage and I thought about splitting up into a 3Tb x 6 raidz2 and a 3Tb x 10 raidz2 .

I have thought further about splitting out my audio flac files into a separate small mirror because they are most likely the reason for the disks to spin up (streaming audio during the day or night).

i recently replaced a failing WD green drive on my 10 drive raidz2 pool, it took 24 h 12 m to resilver. This is with SATA3 and consumer WD Green/Red 3Tb drives. a "wider" raidz3 pool would probably take longer than that, with SATA3 and comparable drives.

Perhaps I should have bought a 4U instead of a 3U SM chassis so I could optimize for the audio streaming case. I am also very interested in the new 8Tb Seagate archive drives. They seem a perfect fit (with some more development) for a COW file system like zfs.