Options for redundant storage cluster?

[Matthew Law]

Hi,

hopefully I'm not too far out posting this question here.  It takes in a
lot of areas so I was unsure where to post it.  If it belongs on another
ML please advise and I will re-post it there.

I am researching options for a two node failover storage cluster. This is
primarily to provide shared storage (either iSCSI or NFS) for XenServer
VMs.  I am looking to get the best bang for the buck and wondering if
FreeBSD might be a good choice?

Hardware-wise we have available two identical supermicro chassis each with
16 x SAS bays and a choice of AMD or latest Xeon 5500 CPUs, together with
as many gigabit cards as we need but the budget won't stretch to faster
networking.  It would be nice to take advantage of ZFS and use two or
three 8-port SAS HBAs in each server rather than expensive hardware RAID
cards.

We don't need to store more than around 2TB but we would like to
comfortably service around a 75 - 100 VM instances (the VMs on average,
are not too I/O heavy).  Thin provisioning and snapshots would be nice,
too.

My initial thoughts were that we might be able to use ZFS, cheap LSI 8
port SAS HBAs together with a dozen or so SATA II drives and a couple of
Intel X25E SSDs to help things along.  It would be great if these boxen
could network boot, so we can use all the drive bays for storage.  I have
no idea what options exist for clustering NFS/redundancy.

I would be very grateful for any advice - especially from anyone who has
experience in the same scenario.

Thanks in advance,

Matt.