it's pretty simple, if i understand it correctly. When you add some blocks
to zfs...
xxxxxxxxxxx
then take a snapshot
xxxxxxxxxxxx
(snapshot of x)
the disk has the space of the x's and the snapshot does't take up any space
yet
then you add more to the drive
and maybe take another snapshot
xxxxxxxxxxxx dddddddd
(snapshot of x)
(+ difference)
(snapshot of d)
each time you change stuff thats part of all the data sets the snapshots
grow (it keeps track of the DIFFERENCES) so they start off small but grow
larger....then, if you DELETE something from your current filesystem it
"falls" to the snapshot....i hope i am explaining it well...but when you
think about it like this it's easy to see how this can happen
On Tue, Aug 18, 2009 at 8:47 AM, Matthew Stevenson <no-re...@opensolaris.org
> wrote:
> > Well, I see USEDSNAP 13.8 GB for the dataset, so if you delete ALL
> > snapshots you'd probably be able to get that much.
>
> I agree, it's just hard to see how...
>
> > As for "which snapshot to delete to get most space",
> > that's a liitle
> > bit tricky. See
> > rpool/export/home/m...@zfs-auto-snap:monthly-2009-06-2
> > 8-20:59, which
> > has USED 2.45G? If I understand correctly, it roughly
> > means
> > rpool/export/home/m...@zfs-auto-snap:monthly-2009-06-2
> > 8-20:59 and
> > rpool/export/home/m...@zfs-auto-snap:monthly-2009-07-0
> > 5-13:43 has
> > about 2.45G of difference.
>
> That's what I thought too, but by that logic I'd have thought that if you
> add up all the "differences", you'd get the total USEDSNAP figure of 13.8GB,
> but you don't - it only adds up to around 5GB.
>
> >
> > This means:
> > - Deleting
> > rpool/export/home/m...@zfs-auto-snap:monthly-2009-06-2
> > 8-20:59
> > only probably won't save you lots of space, as the
> > used space would
> > probably be moved to
> > rpool/export/home/m...@zfs-auto-snap:monthly-2009-05-2
> > 8-08:03
> > - Deleting all snapshot on and prior to
> > rpool/export/home/m...@zfs-auto-snap:monthly-2009-06-2
> > 8-20:59 could
> > give you at least 2.45G space.
>
> Yes, that's exactly what happened - the used data all moved to another
> snapshot, and deleting that snapshot freed it all up (I guess that must have
> been the point at which I first wrote the large files, or whatever). It
> seems that the more you start to delete things, the easier it is to see
> where the total USEDSNAP figure is coming from.
>
> It's almost like it can't tell you where the figure is coming from ahead of
> time - it requires you to take more actions before it can give you a more
> accurate figure. I'm sure there must be a way to find out though...
>
> Thanks,
> Matt
> --
> This message posted from opensolaris.org
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