[PVE-User] Backup in snapshot mode with running sortware

Adam Thompson athompso at athompso.net
Mon Jul 28 20:08:28 CEST 2014


You'll get what's called "crash-consistent", which means the filesystem and database both have to do a consistency check and replay or rollback their journals.
This *usually* works automatically, but many things can cause problems.
Remember that restoring a snapshot is almost exactly equivalent to pulling the plug on a server and then rebooting it (minus the risk of writing corrupt data during the handful of milliseconds the system keeps running with insufficient power)... In other words, if you kill -9'd the KVM process and restarted it, you'd be in exactly the same situation as when restoring a snapshot.
So if your software stack usually handles that kind of failure, it'll also usually handle snapshots properly.  Most systems & software do, nowadays, including ext3 and MySQL.
-Adam

On July 28, 2014 12:56:45 PM CDT, "Luis G. Coralle" <luiscoralle at fi.uncoma.edu.ar> wrote:
>Hi all
>
>I have a question regarding backups.
>Assuming a traditional installation of 3.2 pve a linux vm with qcow2,
>saved
>on disk /dev/mapper/pve-data on /var/lib/vz type ext3
>Assuming I have mysql running on the VM with a large DB. What happens
>when
>a backup is made in snapshot mode of the vm?
>When the backup is restored, the DB is in a consistent state?
>
>
>-- 
>Luis G. Coralle
>
>
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>
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