[Lustre-discuss] Shrinking the mdt volume

[Bob Ball]

root at lmd02 ~# df -i /mnt/tmp
Filesystem            Inodes   IUsed   IFree IUse% Mounted on
/dev/sdb             521142272 46438537 474703735    9% /mnt/tmp

So, it appears I could cut the size by a factor of 5, and still only 
have half the inodes in use.  I guess 500GB is a good, round number in 
that case.  We are mostly bigger file oriented, by policy and active advice.

But, "following the manual verbatim" seems ominous.

bob

On 7/9/2013 9:19 PM, Carlson, Timothy S wrote:
> But how many inodes are in use on the MDT?  If you shrink the volume down you are by default going to have way fewer inodes on the MDT.  For example, my MDT is 450GB and using 31GB or 8% of the space but it is using 17% of the inodes available.
>
> You might have lots of big files in which case you don't have to worry about the inode count but I would check to see how many inodes were in use before you go crazy shrinking things down.
>
> My past experience with the tar/xattr method of doing MDT movements following the manual verbatim has never been successful.. YMMV
>
> Tim
>
> -----Original Message-----
> From: lustre-discuss-bounces at lists.lustre.org [mailto:lustre-discuss-bounces at lists.lustre.org] On Behalf Of Bob Ball
> Sent: Tuesday, July 09, 2013 5:57 PM
> To: hpdd-discuss at lists.01.org; Lustre discussion
> Subject: [Lustre-discuss] Shirinking the mdt volume
>
> 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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