[DRBD-user] Use DRBD and LVM Snapshots to create a point-in-time replica

Ralf Schenk rs at databay.de
Thu Jan 11 12:29:11 CET 2007


Ross S. W. Walker schrieb:
> As the subject says I want to know if it is possible to use DRBD and LVM
> snapshots to create a point-in-time replica?
> 
> This would allow me to rotate snapshots in a pattern that would provide
> the best consistency/coverage for my needs.
> 

Hello !

I do this on a server pair with DRBD 8.0pre6 under XEN. I think you will
have to use DRBD 8.X because only later DRBD Versions claim to run
without problems on top of LVM Volumes.

I snapshot the underlying LVM Volumes readonly and do rsync style
rotating Backups with the help of dirvish (http://www.dirvish.org/). To
have consistent backups of my MySQL Databases I have a small perl-skript
that runs before the backup which commits a "FLUSH TABLES WITH READ
LOCK" to the MySQL Database. After the skript has taken the LVM Snapshot
 via "system" calls I do "UNLOCK TABLES" so the tables are unlocked.
Usually this takes about 1-3 seconds and sessions that attempt to write
to MySQL wait longer for response so that only a short lock can be detected.

Bye
-- 
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Ralf Schenk
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rs at databay.de

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