[BBLISA] ZFS question

[Theo Van Dinter]

Hey folks,

In the past few weeks, I decided to start futzing around w/ ZFS,
since it's been one of those things on my "investigate in copious free
time" list.  And recent mailing list discussions pushed me to actually
get OpenSolaris installed in VMware (which went remarkably well BTW)
to check it out.

I've come across a few things which are fairly annoying, so I wanted
to post here and see what others thought.  The main one stems from the
suggestion that each generic file share, and in this case specifically
homedirs, get individual filesystems via "zfs create".

The reasoning generally boils down that to access the .zfs directory for
snapshots, to limit the user's usage via "set quota", and generally to
give flexibility, you need to deal with the root of the fs.  "set quota"
really just limits the size of the filesystem, which is ok, except
that snapshot space usage is included in that...

If I wanted to give a user, say, a 10G quota on their homedir which
is going to have snapshots, I can't just do "zfs set quota=10G ...".
This is because any file churn and such in the snapshots will eat away
at the user's available space.  Eventually, the FS will be filled w/
user data and snapshots, and the user will complain they can't write to
files anymore.

One thought of how to with this was to simply tack on some generic
percentage to the quota, say 20%, which would allow for snapshots,
ie: 12G.  However, then there's nothing to stop the user from using all
12G, and we're back in the same situation again.  There could also be
a script which monitors usage and deletes snapshots as space fills up,
but that defeats the point of having snapshots around.

What I really want is either a) a way to reserve space from the quota
for snapshots, or otherwise b) a way to not have snapshots count against
the quota at all.  Neither seems possible currently, and so therefore
ZFS seems to have a major flaw.

Have folks run into this?  If yes, what have you done to deal with it?
This feels like the kind of thing which would have been obvious and
handled.  Hopefully I didn't just miss a zfs cli option somewhere.

Thanks. :)


-- 
Theo Van Dinter
Systems Administrator: bblisa.org, kluge.net, google.com, etc.
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