How Large a LUN?
The best way to con gure a LUN for a given VMFS volume is to size for throughput rst and capacity second. That is, you should aggregate the total I/O throughput for all applications or virtual machines that might run on a given shared pool of storage; then make sure you have provisioned enough back-end disk spindles (disk array cache) and appropriate storage service to meet the requirements.
This is actually no di erent from what most system administrators do in a physical environment. It just requires an extra step, to consider when to consolidate a number of workloads onto a single vSphere host or onto a collection of vSphere hosts that are addressing a shared pool of storage.
TECHNICAL WHITE PAPER / 7
Ref: http://www.vmware.com/files/pdf/vmfs-best-practices-wp.pdf
above tech. paper convers following best practice topics
• How large should LUNs be created for a given VMFS volume?
• Should we isolate storage for virtual machines or share a consolidated pool of storage?
• Should we use RDMs or VMFS volumes?
• Should we use disk spanning? If so, are there any concerns or suggestions?
see if this helps.