[Lustre-discuss] Shirinking the mdt volume

Colin Faber colin_faber at xyratex.com
Tue Jul 9 20:49:38 PDT 2013

Hi Bob,

Remember that though actual data usage may be small, the MDT maps out to
many times that with inode spacing requirements.

At a minimum you're required to utilize 1KB spacing with a default spacing
size of 4KB. So the match here is total number of inodes * spacing size ==
total physical disk space required.

That said, with your 1.8 setup, the MDT backup and restore process outlined
within the manual works fine and you should have no problems if you follow


On Tue, Jul 9, 2013 at 6:56 PM, Bob Ball <ball at umich.edu> wrote:

> When we set up our mdt volume, lo these many years past, we did it with
> a 2TB volume.  Overkill.  About 17G is actually in use.
> This is a Lustre 1.8.4 system backed by about 450TB of OST on 8
> servers.  I  would _love_ to shrink this mdt volume to a more manageable
> size, say, 50GB or so, as we are now in a down time before we upgrade to
> Lustre 2.1.6 on SL6.4.  I have taken a "dd" of the volume, and am now in
> the process of doing
> getfattr -R -d -m '.*' -P . > /tmp/mdt_ea.bak
> after which I will do a
> tar czf {backup file}.tgz --sparse
> /bin/tar is the SL5 version tar-1.20-6.x86_64.  This supports the
> --xattrs switch.  So, a choice here, should I instead use the --xattrs
> switch on the tar, or should I use --no-xattrs since the mdt_ea.bak will
> have all of them?
> What are my prospects for success, if I restore that tar file to a
> smaller volume, then apply the attr backup, before I upgrade?
> Answers and advice are greatly appreciated.
> bob
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