ZFS and disk usage

[Johannes Totz]

On 13/04/2012 14:28, Mark Schouten wrote:
> Hi,
> 
> Op Vrijdag, 13-04-2012 om 15:11 schreef Volodymyr Kostyrko:
>>> These are fiesystems that are created with the following
>>> command. zfs create -V ${size}GB ${ZFS_ROOT}/${diskname}
>> 
>> `zfs create -V` withous `-s` creates reserved volume that eats all
>>  needed space immediately. Technically zfs pool is filled only for
>> 23%, but logically you have only 138G left unassigned.
> 
> I understand. However, the created volumes should use a total of
> 1211GB. That's not 1.6TB like zfs list says. But 1211 + 431
> (referred) does come close to 1.6TB.n And 1.6 TB still isn't the
> 1.77TB that's in the zpool.
> 
> I have this feeling that zfs has reserved the space for each volume,
> but counts data written to the volumes in usage of the main
> filesystem. Mainly because zfs list shows me that the volumes have
> only 16KB referenced, where /storage has 431GB referenced.

Without checking the numbers myself...
Note that zpool and zfs do not agree on (free) space accounting: zpool
shows "raw" space, whereas zfs includes metadata overhead for itself.

Small rant: I dont understand why zpool and zfs show different things.
If you have an integrated storage stack then why not show consistent
numbers? Is there any use for this extra (mis-)information that
zpool-vs-zfs provides?