[Linux-cluster] (newbie) mirrored data / cluster ?

[gordan at bobich.net]

On Tue, 1 Apr 2008, Daniel Maher wrote:

>> The non-SAN option would be to use DRBD (http://www.drbd.org) and put
>> NFS, Samba, etc on top of the DRBD partition.
>
> On this topic, consider this paper by Lars Ellenberg :
> http://www.drbd.org/fileadmin/drbd/publications/drbd8.linux-conf.eu.2007.pdf
>
> Where he notes the following :
> "The most inconvenient limitations is currently that DRBD supports only
> two nodes natively."

I'm not 100% sure, but I think this limit is increased in latest 8.0 and 
8.2 releases.

> While this is not a problem in my theoretical two-server setup, should
> we wish to add a third server in the future (which i find highly
> likely), then DRBD will no longer be an appropriate solution.

I'd double check that this is still a limitation. Ask on the DRBD list.

> Furthermore, that same paper seems to suggest that DRBD is best used in
> a primary / secondary relationship, whereas i'm suggesting an
> "all-primary" sort of setup.

That is the way it has been used traditionally with DRBD <= 7.x, but for a 
while now primary/primary operation has been fully supported (obviously, 
you need to use a FS that is aware of such things, such as GFS(2) or 
OCFS(2)).

Gordan