External log mtce

[Murthy Kambhampaty <murthy.kambhampaty@goeci.com>]

I wanted to verify the steps required for moving an external log device for
an xfs filesystem. In my case, I want to move the logdev from an LV on an
md1 to an LV on an md0 on two md1s, with chunk-size of 512k for the md0; the
log device got sunit=2 blocks (8K) from the mkfs.xfs options for the
filesystem.

Step 1.
# log device backup
umount /mnt/fs_xfs1;	dd if=/dev/vg_XFSLOGS/lv_XFSLOG_fs1
of=/mnt/backup/xfslog_fs1 bs=512 

Step 2. 
# log device restore
#(This is just an example that involves restoring the log device to a
different logical volume than previous. It could also be a newly create LV
of the same name as before, but the PV might have changed)
dd if=/mnt/backup/xfslog_fs1 of=/dev/vg_NEW_XFSLOGS/lv_NEW_XFSLOG_fs1 bs=512

# ( I suppose one could reduce Steps 1 and 2 to 
#	umount /mnt/xfs_fs1; dd if=/dev/vg_XFSLOGS/lv_XFSLOG_fs1
of=/dev/vg_NEW_XFSLOGS/lv_NEW_XFSLOG_fs1 bs=512
#  )
	
Step 3. # (re) mount filesystem using restored log device
mount -t xfs -o logdev=/dev/vg_NEW_XFSLOGS/lv_NEW_XFSLOG_fs1
/dev/vg_XFSDATA/lv_XFS_fs1 /mnt/xfs_fs1

Is this correct? Is an intermediate step required for the "new" log device?

Also, is "xfs_growfs -l -L <newsize> /mnt/xfs_fs1" likely to be implemented
anytime soon (without the -i and -x options)? This would, for example,
permit moving to a larger external log device as the filesystem size grew. 

Thanks,
	Murthy


PS: In a recent discussion, Mihail RUSU made the suggestion to archive the
log device, for disaster recovery
(http://marc.theaimsgroup.com/?l=linux-xfs&m=104186705903040&w=2). Err,
won't the data part have the changes in the logdev pretty quickly, making
the logdev backup "obsolete" or at least "inconsistent", so that the only
real option is to mirror the log device?