On Mon, Mar 01, 2010 at 09:34:45PM -0600, Christopher G. Stach II wrote:
----- "Dennis J." dennisml@conversis.de wrote:
What I'm aiming for as a starting point is a 3-4 host cluster with about 10 VMs on each host and a 2 system DRBD based cluster as a redundant storage backend.
That's a good idea.
The question that bugs me is how I can get enough bandwidth between the hosts and the storage to provide the VMs with reasonable I/O performance.
You may also want to investigate whether or not a criss-cross replication setup (1A->2a, 2B->1b) is worth the complexity to you. That will spread the load across two drbd hosts and give you approximately the same fault tolerance at a slightly higher risk. (This is assuming that risk-performance tradeoff is important enough to your project.)
If all the 40 VMs start copying files at the same time that would mean that the bandwidth share for each VM would be tiny.
Would they? It's a possibility, and fun to think about, but what are the chances? You will usually run into this with backups, cron, and other scheduled [non-business load] tasks. These are far cheaper to fix with manually adjusting schedules than any other way, unless you are rolling in dough.
Would I maybe get away with 4 bonded gbit ethernet ports? Would I require fiber channel or 10gbit infrastructure?
Fuck FC, unless you want to get some out of date, used, gently broken, or no-name stuff, or at least until FCoE comes out. (You're probably better off getting unmanaged IB switches and using iSER.)
Can't say if 10GbE would even be enough, but it's probably overkill.
10 Gbit Ethernet makes sense if you need over 110MB/sec throughput with sequential reads/writes with large block sizes.. that's what 1 Gbit ethernet can give you.
If we're talking about random IO, then 1 Gbit ethernet is good/enough for many environments.
Disks are the bottleneck with random IO.
-- Pasi