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I'm building a RAIDZ2 ZFS system, using Ubuntu 13.10 as a base system, and zfsonlinux's packages, having 6 disks dedicated to the pool data and a couple of SSD partitions to do ZIL log and L2ARC cache. My HDDs are all 2.0TB (ie: slightly less than 2.0 TiB) drives.

Yet, once the pool was created, zpool list unexpectedly reports a pool having 10.9T size, 1.93M allocated, and 10.9T free. How is it getting nearly 11T free in a RAIDZ2 having a total of 12.0 of disks? I was expecting to have a mere 8.0T of free space.

Oh, this is apparently a very similar question to ZRAID1 pool size bigger than expected, but about RAIDZ2 instead of RAIDZ... I'll post this anyway, in case anyone cares about RAIDZ2 for their searches.

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It turns out that each drive is 1.82TiB. That, times 6 = 10.9TiB. I suppose zpool reports the total physical space available for filesystem labour (ie: data + parity) as opposed to just the space available for user data without the parity factored in.

In fact, the "duplicate question" has a perfectly good answer already, quoted here (added dashes for clarity):

zpool list - shows the size of the pool, which is the size of all the disks.

zfs list - shows the usable file systems sizes in the pool.

PS. Maybe we should have a "raidz2" tag.

  • (don't use raidz or raidz2!!) – ewwhite Dec 31 '13 at 18:31
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    Because: nex7.blogspot.com/2013/03/readme1st.html - There are serious compromises to using RAIDZ(1,2,3) in your ZFS arrays. Performance, expandability, complexity... – ewwhite Dec 31 '13 at 19:19
  • @ewwhite the article you mentioned did include some limitations performance-wise for building a "raidz(2)", it also included decent advices for someone building a "raidz(2)". There is also compromises in building mirror vdevs, and of course compromises in raidz alternative: soft/hard raid. – tdihp Oct 19 '17 at 2:27

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