[Linux-cluster] Snapshots with GFS1/RHEL 4 (U4)

[Caetano, Greg]

Oliver

What does the following command show for the status of your snapshot
volume and/or device

# lvdisplay /dev/GFS/LV1 


Greg Caetano
HP TSG Linux Solutions Alliances Engineering
Chicago, IL
greg.caetano at hp.com
Red Hat Certified Engineer
RHCE#803004972711193
-----Original Message-----
From: linux-cluster-bounces at redhat.com
[mailto:linux-cluster-bounces at redhat.com] On Behalf Of Oliver Olsen
Sent: Friday, June 22, 2007 12:51 PM
To: linux clustering
Subject: [Linux-cluster] Snapshots with GFS1/RHEL 4 (U4)

Hi,
I'm currently in the process of upgrading a RHEL 3 cluster to RHEL 4,
and I haven't been able to figure out how to use snapshots in a proper
way. We have other RHEL 4 systems using LVM2, and I use snapshots with
ext3 for backup with great success on those. As the demand for uptime on
this particular cluster is cruicial (and regular filebackup using tar is
way too slow!) I was hoping to accomplish the same kind of snapshots
with GFS1 and RHEL 4 as with ext3.

My test-environment consists of 3 VM's in a VMware Server 1.0.3
environment, using DLM and one GFS filesystem on the VM's. Fencing and
connectivity is working just fine, but when I try to use snapshots
things go wrong.

I try to initiate the snapshot via
[root at gfs1 Scripts]# lvcreate -L500M -s -n snap /dev/GFS/LV1 Logical
volume "snap" created

When I try to mount the snapshot (in the same way as I do with an ext3
snapshot) it does not seem to work

[root at gfs1 Scripts]# mount -t gfs
/dev/mapper/GFS-LV1 on /mnt/GFS type gfs (rw)

[root at gfs1 Scripts]# mount -t gfs /dev/GFS/snap /mnt/GFS-snap
mount: File exists

Also - when I try to do changes in the /mnt/GFS filesystem after
creating the snapshot, there does not seem to be any changes in the
snapshot when I check the graphical interface of LVM (it says Snapshot
usage: 0%). Attributes are "swi-a-" and GFS (clustered) according to
LVM.

I assume I am missing something vital here, but I haven't been able to
find the documentation which explains this in an easy manner.
Any inputs will be highly appreciated!

Best regards,
Oliver Olsen

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