This is a FAQ, but the FAQ is not well maintained :-(
http://hub.opensolaris.org/bin/view/Community+Group+zfs/faq
On Feb 8, 2010, at 1:35 PM, Lasse Osterild wrote:
> Hi,
>
> This may well have been covered before but I've not been able to find an
> answer to this particular question.
>
> I've setup a raidz2 test env using files like this:
>
> # mkfile 1g t1 t2 t3 t4 t5 t6 t7 t8 t9 t10 s1 s2
> # zpool create dataPool raidz2 /xvm/t1 /xvm/t2 /xvm/t3 /xvm/t4 /xvm/t5
> # zpool add dataPool raidz2 /xvm/t6 /xvm/t7 /xvm/t8 /xvm/t9 /xvm/t10
> # zpool add dataPool spare /xvm/s1 /xvm/s2
>
> # zpool status dataPool
> pool: dataPool
> state: ONLINE
> scrub: none requested
> config:
>
> NAME STATE READ WRITE CKSUM
> dataPool ONLINE 0 0 0
> raidz2-0 ONLINE 0 0 0
> /xvm/t1 ONLINE 0 0 0
> /xvm/t2 ONLINE 0 0 0
> /xvm/t3 ONLINE 0 0 0
> /xvm/t4 ONLINE 0 0 0
> /xvm/t5 ONLINE 0 0 0
> raidz2-1 ONLINE 0 0 0
> /xvm/t6 ONLINE 0 0 0
> /xvm/t7 ONLINE 0 0 0
> /xvm/t8 ONLINE 0 0 0
> /xvm/t9 ONLINE 0 0 0
> /xvm/t10 ONLINE 0 0 0
> spares
> /xvm/s1 AVAIL
> /xvm/s2 AVAIL
>
> All is good and it works, I then copied a few gigs of data onto the pool and
> checked with zpool list
> r...@vmstor01:/# zpool list
> NAME SIZE ALLOC FREE CAP DEDUP HEALTH ALTROOT
> dataPool 9.94G 4.89G 5.04G 49% 1.00x ONLINE -
>
> Now here's what I don't get, why does it say the poo sizel is 9.94G when it's
> made up of 2 x raidz2 consisting of 1G volumes, it should only be 6G which df
> -h also reports correctly.
No, zpool displays the available pool space. df -h displays something else
entirely.
If you have 10 1GB vdevs, then the total available pool space is 10GB. From the
zpool(1m) man page:
...
size
Total size of the storage pool.
These space usage properties report actual physical space
available to the storage pool. The physical space can be
different from the total amount of space that any contained
datasets can actually use. The amount of space used in a
raidz configuration depends on the characteristics of the
data being written. In addition, ZFS reserves some space for
internal accounting that the zfs(1M) command takes into
account, but the zpool command does not. For non-full pools
of a reasonable size, these effects should be invisible. For
small pools, or pools that are close to being completely
full, these discrepancies may become more noticeable.
...
-- richard
> For a RAIDZ2 pool I find the information, the fact that it's 9.94G and not
> 5.9G, completely useless and misleading, why is parity part of the
> calculation? Also ALLOC seems wrong, there's nothing in the pool except a
> full copy of /usr (just to fill up with test data), it does however correctly
> display that I've used about 50% of the pool. This is a build 131 machine
> btw.
>
> r...@vmstor01:/# df -h /dataPool
> Filesystem Size Used Avail Use% Mounted on
> dataPool 5.9G 3.0G 3.0G 51% /dataPool
>
> Cheers,
>
> - Lasse
>
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