Disappearing available space with ZFS...what am I missing?

[CyberLeo Kitsana]

On 09/29/2010 12:56 AM, Aaron wrote:
> I've created a ZFS pool with zpool create tank raidz ada0 ada1 ada2
> ada3, and then I add some additional mountpoints (I think they're
> called) using zfs create tank/storage, etc. In zpool list, I see the
> pool with 3.62T available. With df -h, I see 2.4T available for tank,
> and tank/storage. When I first created tank, it had the 3.62T
> available as I expected. What am I missing? I do have compression set
> to gzip-9 on tank which gets inherited like I want, don't know if that
> would affect anything.

zpool list shows raw space, and zfs list (and, to a certain extent, df)
shows effective capacity. You've configured a raidz, which chews up
extra space to store the redundant parity information; thus, for a
4-disk raidz, 1GB of stored data will use up about 1.33GB of raw space.

Since effective capacity in ZFS is so variable, due to things like ditto
blocks, raidz, compression, and (soon to be added) dedup, the numbers
provided by df no longer make much sense.

This blog posting can provide further elaboration as to why df doesn't
work for advanced file storage:

http://www.c0t0d0s0.org/archives/6168-df-considered-problematic.html

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