Setting up a VI3 environment with an EMC Clarion CX3-20F with 15 FC 300 GB drives and 45 SATA II 1TB drives. I'm looking for some ideas (best practices) about how to set up the Raid Sets and Luns. For the first phase of the project we are migrating about 25 Windows 2000/2003 servers (with minimal system requirements). Definitely will be doing RAID-5 and eventually VMotion. Anyone out there have some experience to share about how big to make the Raid Sets and how many Luns per?
To answer your question is very difficult since the design will be directly depended on your specific environment – especially the disk access load of every VM.
Firstly you need to look at your hardware. Some hardware will function faster if you create LUNS with a specific number of drives. For example: I know that the EMC CX500 SAN is optimised if you create a RAID group with either 5 or 9 drives.
The number of VM’s that you want to create per LUN is directly dependent on the disk drive load of the VM. If disk access is VERY high you normally will connect a single VM to a LUN on RAID-10. I’ve seen as many as 10 VM’s with very low disk access running on a single LUN (RAID-5) without problems (although not really recommended).
One crucial thing to consider is that size of LUN vs the total size of the VM’s on the LUN. Remember that if you create snapshots it (the delta files) will grow outside of the assigned VM space. If a lot of data is changed during snapshot mode the LUN could fill up causing potential data corruption of all the VM’s on the LUN.
We generally create LUNs of 500GB to 1TB in dedicated RAID groups and then have a max of 10 VMs running on them (some LUNs only have 1 VM). When sizing the LUN remember to leave sufficient space for snapshotting (equivalent to at least the size of the largest VM within that LUN). We also have some SATA drives set aside to snapshot onto as part of our VCB backup process. I wouldn't use SATA drives for hosting production VMs unless they weren't very demanding in terms of I/O (or were test systems). We have Clariion CX3-20c's as our storage and they do fine (although upgrading one to a CX4 as we've run out of disk capacity).