[CentOS] Dell Equallogic

nate centos at linuxpowered.net
Wed Oct 14 18:52:19 UTC 2009


James A. Peltier wrote:

> Mounting a snapshot requires the generation of a new UUID for the file
> system in order to be able to use it.  Perhaps this is a XFS limitation,
> but unlike ZFS they aren't immediately available.  We need to perform this
> action extensively to backup file systems and allow for quick data
> recovery.

Another side effect of snapshots and using LVM for example(applies
to any vendor's block based snapshots), is you can't easily take
a snapshot of an LVM-based file system, then mount that snapshot
on the same system, LVM will bitch. I spent some time trying to
play with dynamically changing the UUID in the volume group but
gave up, too complicated for my needs, instead I just mount the
snapshot on another system(or a VM with either Raw device mapping
in VMware or a software iSCSI initiator on the guest).

I've written a few scripts for things like mysql snapshots and
Oracle snapshots over the years with my 3PAR array, using SSH
and key-based authentication the interface is pretty easy, a single
command to create a read-only snapshot, then another command
to create a read-write (read-write snapshots must be children of
read-only ones in the 3PAR world anyways). The process takes less
than a second, and if I want to snapshot a dozen volumes at the
same instant, still a single command and the array ensures all
volumes are taken at the same point in time, very helpful for
Oracle snapshots which can get messy if your dealing with
multiple volumes and not having them all perfectly in sync
with each other.

nate




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