[DRBD-user] drbd or rsync?

Peter Sabaini peter at sabaini.at
Wed Apr 8 19:13:57 CEST 2009

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

On Wednesday 08 April 2009 18:38:54 you wrote:
> > A crucial factor is wether you can tolerate stale data. Running rsync
> > periodically will probably result in not-quite-uptodate replication when
> > the storm troopers come rushing in and cut your power. If that is not a
> > concern, eg. because your data doesn't change all that often, or you
> > simply don't care about a few lost updates, then rsync is IMHO simpler to
> > set up.
> >
> > In contrast, DRBD does real replication. Depending on your link/network
> > quality and the chosen protocol you can guarantee that local writes are
> > only considered complete if the remote side also has completed.
> Maybe it is a re-incarnation of executive order 6102, to melt down the
> servers for their gold content?
> Anyhow, provided the bandwidth is sufficient, I prefer the DRBD
> option.  However, will the backups be successful, if the backup drive
> is attached to the secondary?  Most of what I've read suggests that
> you shouldn't even mount the secondary in read-only mode (although
> maybe an LVM snapshot can be mounted for taking a backup).

DRBD won't allow you to mount a secondary. This means you either have to use a 
Dual Primary setup (requiring a cluster filesystem) or make a block-level 
backup (don't know if thats adivsable). Maybe you can temporarily disconnect 
DRBD for the backup, promote the secondary, mount + backup, demote again, and 
reconnect -- Im not really sure if this would work though, you'd have to try. 


> For databases, I intend to dump them to text files at least an hour
> before attempting to make a backup of the secondary.  This gives me
> something to fall back on if the raw files are not in a consistent
> state on the secondary.

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