zfs discuss - Jul 2007 - Yet another zfs vs. vxfs comparison...

Hi,

sorry if I am brining up old news, but I couldn''t find a good answer
searching the previous posts (My mom always says I am bad with finding things :)

However I noticed a difference when creating a zfs filesystem compared with a
vxfs filesystem in the available size. ie.

ZFS
zonedata/zfs       [b]392G[/b]   120G   272G    31%    /zfs

VxFS
/dev/vx/dsk/zonedg/zonevol
                       [b]400G[/b]    78M   397G     1%    /vxfs

They are both build from 4 LUNs of the same size from the same array....
So where did the 8G''s go?

thanks,

//Mike
 
 
This message posted from opensolaris.org

Ive heard it is hard to give an correct estimate of the used bytes in ZFS,
because of this and that. It gives you only an approximate number. I think Ive
read that in the ZFS administration guide somewhere in the "zpool
status" or "zfs list" command?
 
 
This message posted from opensolaris.org

Hi,

thanks for the reply. But there must be a better explanation other than that?
Otherwise it seems kinda harsh to "loose" 20GB per 1TB and I will most
likely have to answer this question when we are going to discuss if we are to
migrate to zfs over vxfs..
 
 
This message posted from opensolaris.org

Orvar Korvar wrote:
> Ive heard it is hard to give an correct estimate of the used bytes in ZFS,
> because of this and that. It gives you only an approximate number. I think
> Ive read that in the ZFS administration guide somewhere in the "zpool
> status" or "zfs list" command?
That is not correct; the amount of space used is accurate.  However, as 
documented in the zfs(1m) manpage, it reflects the space currently used on 
disk, and not any pending changes.  So for example after writing / deleting a 
file, the space used may not reflect the change until a few seconds have passed.

--matt

Mikael Kjerrman wrote:
> Hi,
> 
> sorry if I am brining up old news, but I couldn''t find a good
answer searching the previous posts (My mom always says I am bad with finding
things :)
> 
> However I noticed a difference when creating a zfs filesystem compared with
a vxfs filesystem in the available size. ie.
> 
> ZFS
> zonedata/zfs       [b]392G[/b]   120G   272G    31%    /zfs
ZFS sets aside some space for allocation efficiency (about 1.6% -- see 
dsl_pool_adjustedsize()).

Note that "zpool list" will show the amount of space actually
used/free,
without taking into account this set-aside space, quotas, or reservations.

--matt