Anyone considering a new virtualization setup should read that and be pretty much ready to go.Quote:
SANs are, in general, more suited to larger setups (probably half a dozen or more processing nodes), just because it takes some economics of scale to make them worthwhile - decent speed / latency connections between VMs and their virtual harddrives (i.e. preferablly fibre channel) and failover (i.e. preferably mirrored SAN hardware). For the average school (or, indeed, small business) setup I'd aim to use local storage on each processing node. You can have instant failover by real-time mirroring volumes between physical machines - set the machines up in pairs, preferably in different physical locations for extra security, and have them mirror each other's virtual machine volumes. In the past I've used Xen and DRBD for this, and this is my current home server setup, and it can allow for good instant-recovery abilities.
However, in my experience, most schools and smaller businesses don't actually need proper, millisecond-response failover. Sudden, unexpected, catastophic hardware failure should, hopefully, be very rare, and a few minutes of downtime while you boot up VMs on another machine are generally perfectly acceptable. This gets rid of the need for real-time mirroring of virtual machine images in exchange for taking regular backup snapshots instead and having those snapshots exported to a different storage volume. This is also rather easier to set up as a proper backup solution, with previous versions of virtual machine images available in case of disaster or configuration problems.
I'd use that Dell R510 as your main VM host, hosting your Domain Controller, print server, MIS server and general applications server(s) on local storage. Give the R310 an equal amount of local storage and have it regularly take backup snapshots from the R510 (have the R310 host another domain controller, though, don't take images of the first domain controller, DCs don't restore well from image backups as they use a lot of time-sensitive data). You can host as many extra VMs as you can fit on, although you might want to bear in mind that if one machine conks out one day you'll want to be able to run a minimally functional system on one machine.
Use one of your other servers as a dedicated file server for user files - we've found FreeNAS to work well, with a nice, GUI-based interface and support for ZFS. Bear in mind that ZFS' best feature, block-level deduplication, takes a lot of RAM - your file server might need 8GB or more of RAM and a decent processor to make best use of ZFS. Have another dedicated server, with at least 1.5 times the file server's storage size, as a backup for the file server, with regular snapshots or backups available so users can get to previous versions of files.