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.
I'm not sure I understand; would it be correct for me to restate the
above as:
"The set of filesystem volumes that would be needed to support each VO
do not necessarily map simply to the underlying physical volumes. Thus
LVM may not help?"
(Or have I completely misunderstood?)
LVM provides a facility where individual physical volumes can be grouped
into Volume Groups. Logical volumes can then be added to volume groups
-- and later deleted or resized as necessary.
An example may help illustrate:
------------------------------------------------------------------------
Say I'm an Tier-2 sysadmin with 3 RAID 4TB arrays - sda, sdb, sdc. If
I'm using LVM, I can simply create a new Volume Group called "SE1" and
add the three RAID arrays to it.
This provides me with a new 12TB volume group. I can now create
individual logical volumes in this group, one for each VO I support --
eg "atlas", "alice", "dteam", "cms", etc. Let's say I allocate 512GB to
each logical volume to begin with.
I can then create filesystems in these individual logical volumes and
mount them on my SE pool node(s). I can then set up individual DPM (or
dCache) pools and point them at each of my newly created logical volumes
-- setting per-VO access controls appropriately.
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.[*]
------------------------------------------------------------------------
The important thing to realise here is this: Logical Volumes don't have
to be contiguous on disk. They can even occupy several sections of
multiple different Physical Volumes; it doesn't matter.
Cheers,
David
[*] Assuming that tools exist to shrink the filesystem. This is not
uniformly the case!
--
David McBride <[log in to unmask]>
Department of Computing, Imperial College, London
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