[DRBD-user] drbd vs GFS/GNDB

Lars Ellenberg Lars.Ellenberg at linbit.com
Tue Jul 6 12:47:14 CEST 2004

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


/ 2004-07-02 17:16:31 -0400
\ Greg Freemyer:
> I'm not a DRBD expert, but I do know snapshots and advanced backup
> strategies.
> 
> Maybe you could use DRBD to create "snapshots"?  They are often used to
> provide read-only copies of volumes for backup/testing/data mining/load
> sharing.

have a look at the thread(s) about drbd and lvm and snapshots a few
weeks ago.

> In particular if backups are your only issue, maybe you could do
> something like the below:
>
> 1) Quiese application on primary
> 2) Flush filesystem cache to disk and stop filesystem i/o
> 3) stop drbd replication from master to secondary.
> 4) re-enable filesystem i/o
> 5) Allow application to restart
> 6) On secondary mount drbd volume read-only
> 7) On secondary perform backup
> 8) On secondary unmount drbd volume
> 9) restart drbd replication
> 
> Comments:
> step 1) This is commonly required with snapshots, so it should be fairly
> easy.  Typically databases etc. have way to signal them to prepare for
> snapshot.
> 
> step 2) I know XFS supports the filesystem i/o freeze/unfreeze concept
> form user-space.  I'm not sure about others.
> 
> step 3) I'm not a drbd expert, but I assume this is easy

on_secondary# /etc/init.d/drbd stop

> step 9) With drbd 0.7, only the dirty blocks should need to be copied
> between the servers, so the load should not be too bad.

on_secondary# /etc/init.d/drbd start

as long as the primary stays up, 0.6 does a "SyncingQuick", too.

	lge



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