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I would go for 3x 8 drives in raidz2
Resilver performance is critical. And resilvering with ZFS is dog slow!
I have 5 x 2TB drives in raidz1 and have used about 50% of the pool space. Resilvering takes around 12 hours now.
Performance is good, I still get over 300MB/s read and 100MB/s write. But there are a lot of snapshots that are created and deleted every day and around 100GB of the storage has deduplication enabled.
I expect the resilver/scrub time to be even higher as times moves on. When I hit 48 hours resilver/scrub time I will copy the pool over to a new pool to "reset" the "fragmentation".
ZFS is a real beast! But it really needs the block pointer rewrite feature.
Is the recommendation still to have zPools with 9 or less disks? I'm about to setup 24 drives and would like to do 2 RaidZ2 pools of 12 disks each.
Assume you mean VDEV?
Cos the limit of a zpool is: (quoted from Wikipedia)
256 zettabytes (278 bytes) Maximum size of any zpool
As i understand, the performance issues with 4K disks isn't just partition alignment, but also an issue with RAID-Z's variable stripe size.
RAID-Z basically works to spread the 128KiB recordsizie upon on its data disks. That would lead to a formula like:
128KiB / (nr_of_drives - parity_drives) = maximum (default) variable stripe size
Let's do some examples:
3-disk RAID-Z = 128KiB / 2 = 64KiB = good
4-disk RAID-Z = 128KiB / 3 = ~43KiB = BAD!
5-disk RAID-Z = 128KiB / 4 = 32KiB = good
9-disk RAID-Z = 128KiB / 8 = 16KiB = good
4-disk RAID-Z2 = 128KiB / 2 = 64KiB = good
5-disk RAID-Z2 = 128KiB / 3 = ~43KiB = BAD!
6-disk RAID-Z2 = 128KiB / 4 = 32KiB = good
10-disk RAID-Z2 = 128KiB / 8 = 16KiB = good
I'm about to test this theory with the help of some people's new NAS hardware. So i should have some performance numbers soon that can verify this. Still wanted to post it here already.
You might want to rethink this 12 devices per vdev thing. Check out this thread:
http://arstechnica.com/civis/viewtopic.php?p=20797605
In particular, check out this quote from that thread (sub.mesa)