[Gluster-users] Bricks suggestions

[Arnold Krille]

On Thursday 03 May 2012 11:52:13 you wrote:
> 2012/5/2 Arnold Krille <arnold at arnoldarts.de>
> > As far as I understand it (and for the current stable 3.2) there are two
> > ways
> > depending on what you want:
> >  When you want a third copy of the data, it seems you can't simply
> >  increase
> > the replication-level and add a brick. Instead you have to stop usage,
> > delete
> > the volume (without deleting the underlying bricks of course) and then
> > rebuild
> > the volume with the new number of replication and bricks. Then self-heal
> > should do the trick and copy the data onto the third machine.
> I can't stop a production volume used by many customers.

Yes you can. There are scheduled maintainance-times. Unless your SLA is about 
100% availability (in which case you are f***ed as every outage will make you 
miss your SLA).

And the outage I outlined should be something like 30s when done by a (tested) 
script, 1-2min when done by hand. Could be that you can even keep it mounted 
(as glusterfs) on the clients. Though I haven't tested this.

> I think that the best way should start with the correct number of
> replication nodes
> even if one of these node is not present.

Good luck with that. While you can do that with software-raid and with drbd, 
you can't do that with gluster. When you create a volume with replication set, 
it only accepts multiple of that replication for the number of bricks.
I am told that 3.3 will have the ability to change the replication-level while 
the volume is up. And I think I was even promised dynamic replication from the 
kind "here are three bricks, give me two replicas of everything".

> In this way, the volume is created properly, and when needed I have to just
> add the new machine and trigger the self-healing.

Either wait for 3.3 or do the distributed-replicated-volume way I outlined 
earlier.

Have fun,

Arnold
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