On Wed, Jun 14, 2006 at 11:51:10AM +0100, David McBride wrote:
> On Wed, 2006-06-14 at 09:59 +0100, Steve Traylen wrote:
>
> > > I haven't been following the entire thread, but would it not be possible
> > > to use an LVM[0] to partition the available physical space into
> > > partitions, one (or more) for each VO?
> >
> > The spaces don't nescesarily correspond to physical devices. The size of
> > each space, a directory is specified at creation time though can be expanded,
> > I expect they can be reduced as well occupency permitting.
>
> See? Each VO is now effectively quota'd to 512GB of storage. If I
> later want to increase the quota for a VO, I can simply _enlarge_ the
> corresponding logical volume and the filesystem it contains, providing
> more space. If I want to decrease an allocation, I can shrink that
> volume.[*]
You do not need a filesystem per pool (in dcache at least), you
can simply create directories per pool and give the pool any size
you want, nothing stops you from resizing it if it has enough free
space.
The problem (LVM or not) is that you can not reduce a pool or volume
if all the data is used. Having quotas will help to force a VO to do
something about the extra data if they want to be able to write.
Using LVM or not doesn't change this and at least ext3 resizing is
problematic if you want to go from 500M to 2TB or the other way around,
having a few million inodes in every 500M volume so you can resize
to something a lot bigger in the future isn't the very best solution.
Of course having on each disk server one pool per VO is a problem as
well, some people here plan or have already hundreds of disks servers
which will put the number of pools in the thousands. I am not even sure
that dcache can handle that amount of pools and even worst it will also
affect the number of movers,calculations about load,etc. on each machine
for no reason.
What I am looking for (and other people I suspect) is having quotas
for each pool so we can manage usage at that level instead of creating
more pools every time we need a new VO. Having a script that will also
rellocate files to a different pool for a pool that the VO uses more
than it's quota will also be nice :)
Cheers,
Kostas
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