[ClusterLabs] snapshots in a clvm environment - some questions for proceeding

Lentes, Bernd bernd.lentes at helmholtz-muenchen.de
Fri Feb 24 18:27:22 EST 2017

----- On Feb 24, 2017, at 7:20 PM, Digimer lists at alteeve.ca wrote:

>> I read
>> https://www.centos.org/docs/5/html/Cluster_Logical_Volume_Manager/cluster_activation.html
>> .
>> It seems that a local activation is not an exclusiv one. Ok. I tried "lvchange
>> -vaey" for that lv, but got:
>> lvchange    Using logical volume(s) on command line
>> lvchange    Activating logical volume "lv_cluster_01" exclusively
>> lvchange  Error locking on node 40a86414: Device or resource busy
>> I shut down the guest, still the same message.
>> Bernd

> In my experience, you had to inactivate the LVs on both nodes, then
> re-activate as exclusive on the one node before you could do snapshots.
> This required powering off the guest server.

I did it and it worked.

> Aside from this, I strongly recommend against snapshots as a backup
> mechanism anyway. There is no way to ensure that that operating system
> and applications are in a clean state when you take the snapshot, so
> using the image is like recovering from sudden power loss. If data was
> in cache but not flushed out, you could have corruption.

I don't want the snapshot for backup, but create it before configuration changes in the vm. 
Or installing some software. To revert if s.th. goes wrong.

> If you can't stop your VMs, I'd recommend using a backup applicationß
> inside the VM that knows how to ensure that your apps and the OS are in
> a clean state, particularly for DBs.

DB's are backuped totally indepently from the snapshotting with their respective tools
like mysqldump or pg_dump.

lvs or lvscan shows which lv's are active and which not.

But what is when i want to have my vm high available again ?
For that all lv's must be active. So snapshot and vm high available is an exclusiv or (exor) ?


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