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

Digimer lists at alteeve.ca
Fri Feb 24 18:49:35 EST 2017

On 24/02/17 06:27 PM, Lentes, Bernd wrote:
> ----- 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) ?
> Bernd

Effectively, yes, they are exclusive.

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