We are purchasing our first SAN, a Dell MD3220 with 24x 146GB 15K 2.5" SAS disks. Because I have little experience with SANs, I'm seeking input on the recommended configuration for these disks.
We have 200 desktops, all are virtualized and rely on Citrix PVS for reads. Writes are redirected locally (and lost on reboot), except for profile changes, which are streamed to/from our file server (2008R2 Server Core) as needed. Citrix recommends RAID 5/6 for PVS, but it seems like a better idea to use RAID 10 for my file server.
We also have a virtualized Exchange 2010Sp1 setup for 120 users, but only concurrent usage of ~ 75. Our AD VM also holds data for about 120 users, as well as providing DNS/DHCP/NPS for all 200 users. It seems like RAID 10 is the best idea here, as well.
We also run about 10 other VMs, including 2 XenApp VMs (1 for hosting, 1 for streaming/management), vCenter (we are 100% virtualized on servers and desktops) for 3 hosts, and small application servers.
We do use PerfectDisk to defrag all our VMs.
It is my understanding that disk groups are assigned to controllers, and in this regard, it seems like my best option to get maximum performance is to create a RAID 10 group for Exchange, AD, file server and XA published, as well as a RAID 5/6 (we have a cold spare) for Citrix PVS, XA streamed, and the rest of my small application servers. Each group would be assigned to its' own controller.
Thoughts/suggestions/comments? One idea I had was to disable the read cache on the MD3220, dedicate all cache to writes, and increase RAM in each my VMs to utilize Windows' caching (we are around 25% RAM utilization on all 3 hosts, <8% CPU).
We will not be using SAN snapshots or virtual disk copies, but may purchase the performance software if budget allows.