Re: [Xen-users] small cluster storage configuration?

[Miles Fidelman <mfidelman@xxxxxxxxxxxxxxxx>]

John Madden wrote:
> > I now have 2 new servers - each with a lot more memory, faster CPUs (and
> > more cores), also 4 drives each.  So I'm wondering what's my best option
> > for wiring the 4 machines together as a platform to run VMs on.
> A few things come to mind:
>
> - Since these two new boxes are so much better, do you really need all 
> four systems for hosting VM's?  If you can do everything on the two 
> old systems, you can do it all on the new systems.  If you just keep 
> it to two nodes, you eliminate some complexity.
I'm mixing development with production, and working on some server-side 
software intended to work across large numbers of nodes - so I figure 4 
machines gives us some more flexibility.  I'm also thinking of keeping 
some of our current production stuff (mostly mailing lists) on the old 
systems - but setting things up to make it easier to migrate later.  
(But, yes, I have thought of it :-)
> - Ever worked with GlusterFS?  It'll allow you to stripe and replicate 
> across multiple nodes.
That's pretty much the only thing that's jumping out, as I peruse the 
net looking for relatively mature solutions.  The one thing that looks a 
little closer is Sheepdog - but it's KVM-only and not all that mature.
One thing I've been wondering about - can't find in the documentation - 
and guess I might just have to start experimenting - is what GlusterFS 
does regarding disks on the same node, vs. disks on different nodes.  
Things like:
- whether or not to run RAID on each node, as well as configuring 
GlusterFS to stripe/replicate across nodes (i.e., with a total of 16 
drives, but split 4-per-node, will Gluster replicate/stripe so that a 
node failure won't kill you)
- what happens to performance if you stripe/replicate across nodes?

Have you (or anybody) had much experience with GlusterFS in practice?  
Particularly on a relatively small cluster?  Comments? Suggestions?
Thought of these....
> - If I/O isn't too much of an issue, you could use one pair with DRDB 
> as the storage node and export to the other two over NFS/etc.
Thought about this, but it would leave half my disk space idle.

> - Export everything over iSCSI, use md to mirror, name everything 
> carefully so you know which nodes you can take down based on where 
> VM's are.  Complicated, but workable.  I suppose you could set this up 
> with DRDB too.
Been thinking about this one too.  The complexity really scares me.  Any 
thoughts re. tools that might simplify things, and/or performance 
implications of using md to mirror across iSCSI mounts on different 
machines?
Thanks again to all,

Miles Fidelman




--
In theory, there is no difference between theory and practice.
In<fnord>  practice, there is.   .... Yogi Berra



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