ZFS vdev and RAIDZ2 question

[twinhardballers]

Hey guys,

I have a norco 4224 and it has 6x2TB hdds in RAIDZ2 in it atm. I was looking to expand to 12 HDDS in the near future.

My question is: If I add another vdev with another 6 hdds in it, do 2 of the hdds from the new vdev go into parity or does it expand and just add them to the total storage keeping 2 drives worth of parity over the 12 drives?

I had a look around online but there doesn't seem to be a definitive answer, and the wiki page is quite vague.


Thanks in advance

[Speedster20]

Each vdev is independent, therefore each raidz2 will have (n-2) space for data. After adding it to the same pool new data will be striped across both vdevs

[twinhardballers]

so if i have 12 disks, 6 in one vdev and 6 in another, i will only get 8 disks worth of storage?

[damox]

Originally Posted by twinhardballers

so if i have 12 disks, 6 in one vdev and 6 in another, i will only get 8 disks worth of storage?

Correct. You will have the equivalent of a RAID60.

[twinhardballers]

that's pretty inconvenient sucks that you can't just add to existing vdevs, probably should have thought about that before going zfs, everyone is raving about it online i thought i'd give it a go, probably a standard raid6 would have been a better choice :P

[Stanza]

Originally Posted by twinhardballers

so if i have 12 disks, 6 in one vdev and 6 in another, i will only get 8 disks worth of storage?

Don't think of it as ONLY 9 Drives worth of storage..

think of it as 4 Drives worth of protection

.

[twinhardballers]

I'll be happy if i have 3-4 drives fail i'm sure :P

edit: there are 24 hard drive slots, and i've used 6 of them, leaving 18. Is it possible to have a single raidz2 vdev with 18 hdds in it to only have to have 4 parity drives? also is it possible to have the remaining 18 drives in 2 9 drive vdevs to have 6 parity drives? if i end up with 4x6 drive vdevs, i'm looking at 8 parity drives....

[pher0x]

If you're not too concerned about data loss/drive failures - why not just use raidz instead of raidz2?

[twinhardballers]

Is it possible to have a zpool with vdevs which are RAIDZ and RAIDZ2?

[BAK]

If I had a Norco (one can plan...) I'd be going with 3 8 Drive (6+2) RaidZ2 vdevs. That way with all 24 drives you'd have 6 drives for parity and still 18 drives for data.

My advice is instead of getting another 6 drives, get 8 instead. Make it a 6+2 RaidZ2, move all your data across to it - then grab another two drives, destroy and rebuild the original 6 drive array into an 8 as well and add it to the pool.

[twinhardballers]

That is almost exactly what I was thinking, great advice, I might do that

[sreg0r]

Originally Posted by twinhardballers

Is it possible to have a zpool with vdevs which are RAIDZ and RAIDZ2?

Yes you can have any combination of vdevs in a pool. Not sure how it handles writing new data though.