[linux-lvm] LVM snapshots and filesystem quiescence

[Clay Gerrard]

I love this question.  I always thought the only way to guarantee a
consistent snap of a block was to unmount it before taking the snap, mostly
just cause of un-fsynced data in the page cache.  Any other answer would be
very welcome.

-Clay


On Thu, Apr 25, 2013 at 5:14 AM, Tanstaafl <tanstaafl at libertytrek.org>wrote:

> Hello,
>
> I'm totally new to LVM snapshots. I've have read the FAQ and docs and
> searched the list archives and can't find an answer to my question...
>
> I know that you have to quiesce SQL databases using their own native tools
> if you want to have a consistent snapshot of the raw db files, but what
> about other programs like postfix or dovecot that are constantly (on a busy
> server) writing to disk? Do you need to stop these, take the snapshot, then
> restart them? Or will the filesystem itself handle this (similar to how VSS
> works on windows)?
>
> I'm fairly certain the answer is no, I don't have to worry about these
> kinds of programs, only SQL databases.
>
> I engage a script that simply performs a native dump of my databases
> immediately preceding the snapshot (my db's are very small and the dumps
> only take a few seconds, and this just seems much simpler to me) and places
> these files into a sql_dumps directory on the filesystem that will be
> snapshotted so these will be included in my backups, so am not worried
> about them being in a consistent state.
>
> Thanks in advance...
>
> Charles
>
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