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Re: [linux-lvm] LVM snapshots and filesystem quiescence



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 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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