Virtualise everything.
Its not just down to the Virtualisation layer, its about the network and way you design and configure the storage.
We use ESX 3.5 with Falconstor's IPstor product to virtualise a Hitachi AMS1000 san with 15 shelves of fibre channel disk and SATA for tier 2 storage, on that we have Exchange, file servers, DB servers and app server guests serving 450+ users.
DAS is as good as local storage but a good RAID card is a must.
Im looking at using 2 DL385 G5p at each of our remote sites using ISCSI SAN software so we can move guests around automagically in event of hardware failure - each box has 8 x 146gb SCSI disks, 2 x quad core AMD and 16gb RAM - performance is very good, way better than the outgoing DL380 G4s there replacing.
With the DL385 G5p you can have additional 8 disks giving 16, thats a good chunk of IOPs!
http://communities.vmware.com/docs/DOC-8760 - Fantastic ESX script that backups Vm's on the fly with no down time, thin provisioning so the backed up size is only what the disk is using rather than the whole disk size.
http://www.rocketdivision.com/wind.html - ISCSI target and initiator - useful free version for presenting disk to ESX and other servers.
http://www.phdvirtual.com/component/jdownloads/?task=view.download&cid=10 - Free ISCSI SAN, simply awesome. Two nodes only for now, 4 in Q3/Q4 this year. < very good free option.
http://www.compaq.com/storage/highlights/lefthandsans.html - HP iSCSI SAN solution, good support and with special bid comes in at 2.4k per node and you can have upto 4 nodes.
