[DRBD-user] Dual-Head as ro?

Lars Ellenberg lars.ellenberg at linbit.com
Tue Dec 9 16:40:50 CET 2014

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

On Tue, Dec 02, 2014 at 02:36:05PM +0100, Christian Völker wrote:
> Hi All,
> >
> >>
> >> Is it possible to run a two-node setup
> > Yes.
> >
> >> *without* a clustered filesystem
> > No.
> Thought so. Never mind.
> > But, what do you really want to solve, what exactly is the challenge?
> > Lars 
> Well, I need to connect two sites. As money is the limiting factor we
> can not have more than a 10Mbit line which makes access to the files
> very slow for one site.  Using clustered file system with drbd allowing
> write access to both will afaik slow down (at least write) access for
> both. No good. So I was thinking to teach the users and tell them to
> have only a read-only share which is fast as it is connected through
> drbd with local storage and in case they need to write use a different

look for nfs + fscache maybe.
At least its intended use case is "almost" what you apparently want.

> volume (which micht be shared through NFSv4). But as even the ro access
> is not working this is not a solution, too.
> Second I was thinking to use drbd in some way as a backup helper. Main
> site runs an ESXi host and I want to perform image backupcs of some VMs.
> Backup is best to be stored on the second site. I was going to use
> something like ghettoVCB to split the hughe image files into smaller
> chunks. As a second idea I was thinking if I could rsync to a drbd
> device which then transfers only the changed bytes to the other site
> with the help of drbd- where the backup tool can copy them.

DRBD is block level, not byte level, and it does no "comparison" between
old and new data, but simply replicate everything you throw at it.

If you rsync anyways, leave off the DRBD layer,
you will have much less traffic.

: Lars Ellenberg
: http://www.LINBIT.com | Your Way to High Availability
: DRBD, Linux-HA  and  Pacemaker support and consulting

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