[Lustre-discuss] MDT backup

[Kalpak Shah]

On Mon, 2009-03-16 at 13:43 -0700, Jim Garlick wrote:
> On Tue, Feb 03, 2009 at 11:47:37PM +0530, Kalpak Shah wrote:
> > On Tue, 2009-02-03 at 10:57 -0700, Nathan Dauchy wrote:
> > > Brian J. Murrell wrote:
> > > > On Mon, 2009-01-19 at 22:46 -0600, Alex Kulyavtsev wrote:
> > > >> Hi,
> > > >> what is the right way to backup MDT ?
> > > > 
> > > > I think this is covered in the operations manual.
> > > > 
> > > 
> > > The manual does indeed cover backups:
> > > http:// manual.lustre.org/manual/LustreManual16_HTML/BackupAndRestore.html
> > > 
> > > It includes this step:
> > > 
> > > >  3. Back up the EAs, run:
> > > > getfattr -R -d -m '.*' -P . > ea.bak
> > > > 
> > > 
> > > Is that necessary for newer versions of tar that support the "-xattrs"
> > > option?  From the man page (I have GNU tar 1.15.1):
> > > 
> > > --xattrs	this  option  causes  tar  to  store  each  file's
> > > 		extended  attributes in the archive. This option also
> > > 		enables --acls and--selinux if they haven't been
> > > 		set already, due to the fact that the data for those
> > > 		are stored in special xattrs.
> > > 
> > > Also, AFAIK, cpio will archive extended attributes as well.
> > > 
> > > Is either 'tar --xattrs' or 'cpio' sufficient for capturing all the
> > > Lustre MDT information?  Would that eliminate the need for the
> > > 'getfattr' step, and cut the time for backup almost in half by requiring
> > > only one pass through the filesystem?
> > 
> > The "tar" package shipped with distros cannot recognize "lustre."
> > extended attributes and hence cannot be used for Lustre backups.
> > 
> > You will need to use Lustre patched tar available for download at
> > http:// downloads.lustre.org/public/tools/lustre-tar/
> 
> I just did some testing with rsync-2.6.8-3.1 from rhel 5 and it appears
> to support Lustre's extended attributes with its -X (--xattrs) option.
> 
> The test I ran was as follows:
> 
> See if initial copy looks correct:
> - create some files in lustre (nonzero length)
> - stop lustre and remount mdt with -t ldiskfs on /mnt/lustre/mdt
> - create an ldiskfs file system on the MDS with -Oext_attr and mount
>   on /mnt/lustre/mdt-backup
> - rsync -Xav --delete /mnt/lustre/mdt/ /mnt/lustre/mdt-backup
> - verify with getfattr -d -m '.*' -P that attrs are identical on all files
>   in both copies
> 
> Make sure rsync updates file/dir if only attrs change
> - unmount /mnt/lustre/mdt and restart lustre
> - run lfs setstripe --count -1 on an existing directory in lustre
> - stop lustre and remount mdt with -t ldiskfs on /mnt/lustre/mdt
> - verify with getfattr that attrs differ on that dir in both copies
> - repeat rsync
> - verify with getfattr that attrs are identical on that dir in both copies
> 
> Verify that a restore works:
> - rm -rf /mnt/lustre/mdt/*
> - rsync -Xav --delete /mnt/lustre/mdt-backup/ /mnt/lustre/mdt
> - unmount /mnt/lustre/mdt and restart lustre
> - verify that md5sums of files created in first test match originals

Is the file restored with the same striping pattern as it was archived
with?

Anyways, its good to know that rsync can backup Lustre attributes, we
can think about modifying rsync to restore striping parameters as well.

Thanks,
Kalpak