Re: [Evms-cluster] Expanding OCFS2 Partition after LUN has been increased in size

[Steve D. <st...@us...>]

"Jason Ngim" <jas...@os...> wrote on 04/13/2009 07:01:37 AM:

> "Jason Ngim" <jas...@os...>
> 04/13/2009 07:01 AM
>
> To
>
> <evm...@li...>
>
> cc
>
> Subject
>
> [Evms-cluster] Expanding OCFS2 Partition after LUN has been increased in
size
>
> Dear Gurus
>
> I have a SAN storage connected to 2 servers using Fibre Optics.
>
> In it i have created 4 LUNs. for future expansions, the LUNS will be
> resized to be bigger, and the OCFS2 partition will also be expanded.
> Please tell me how i can achieve it using EVMS.
>
> example:
>
> before
> /dev/sdb  50GB
>    /dev/sdb1 50GB  (formated using OCFS2)
>
> after
> /dev/sdb  100GB
>   /dev/sdb1 100GB (size is also expanded not creating another
> logical partition)
>
> i would like to know how i can configure so that the /dev/sdb1 can
> be logically expanded to the new size.
> Thank you very much!!
>

> Best Regards
> Jason

Hi, Jim.

Sorry for the late reply.

The normal way you would go about expanding a volume is to target/select
the volume for expansion rather than the segment.  That is, one might
initially think of expanding the segment, e.g., /dev/sdb1, first.  However,
since EVMS coordinates the expansion of the segment with the expansion of
the volume, it needs to know the volume that is being expanded.  After all,
that is what you want in the end is a bigger volume.

After that explanation, here is the bad news.  Looking at the source code
for the OCFS2 plug-in for EVMS, I see that it does not support expanding or
shrinking a volume.  :(  I assume that at the time the author wrote the
plug-in that OCFS2 did not support changing the size of a volume.  Looking
on the web I see that the tune.ocfs2 utility is supposed to allow you to
change the volume size, among other things.  For now, you will have to
expand the volume by hand -- use fdisk to expand /dev/sdb1 and then use
tune.ocfs2 to expand the OCFS2 volume.  You will have to do that outside of
EVMS, i.e., don't be running EVMS at the same time you do the expansion.
EVMS will not pick up the changes if you do.  EVMS should pick up the
changes from your manual expansion the next time it is started.  This will
work if you did a mkfs of OCFS2 on the "compatibility
volume" /dev/evms/sdb1.  That is, you did not make an "EVMS volume"
from /dev/sdb1 and then put OCFS2 on the EVMS volume.

If you made /dev/sdb1 into an EVMS volume then the procedure gets more
complicated.  The metadata for the EVMS volume will need to be migrated for
the new volume size.  (EVMS volume metadata appears at the end of the
device.)  If you are OK with backing up and restoring your data, the
simplest thing to do would be:
1. Backup the data.
2. Delete the OCFS2 volume.
3. Expand /dev/sdb1.
4. Recreate the EVMS volume from /dev sdb1.
5. Put OCFS2 on the volume.
6. Restore your data.

If you need to leave your data intact, the following procedure should work
(off the top of my head, no testing, no guarantees):
1. Backup the data, just in case.
2. With EVMS not running, use fdisk to expand /dev/sdb1.
3. Temporarily move /lib/evms/<evms-version>/ocfs2* out of
the /lib/evms/<evms-version>/ directory so that EVMS will not load the
plug-in adn therefore will not be able to recognize /dev/sdb1 as an OCFS2
volume.
4. Start EVMS.
5. Recreate the EVMS volume from /dev/sdb1.  This will put the EVMS volume
metadata at the end of /dev/sdb1.
6. Save the changes.  You will now have a volume /dev/evms/<name>.
7. Run tune.ocfs2 on /dev/evms/<name> to set the new size.  Do not run
tune.ocfs2 on /dev/sdb1 or it will most likely blow away the EVMS volume
metadata at the end of /dev/sdb1.
8. Move the OCFS2 plug-in back into the /lib/evms/<evms-version>/
directory.
9. Now when you start EVMS again you should see the OCFS2 volume with the
new size.

Your other option is to write up a patch for the OCFS2 plug-in to give it
the ability to resize OCFS2 volumes. :)

Hope this helps.

Steve D.