VMware ESX host need to have storage available before create VMs. Normally the storage is a LUN created on SAN. The question is, what is the best size for a single LUN (storage) in ESX?

Our design for a storage on ESX is 300GB, allow maximum VMFS up to 256GB.

The reasons behind are:

  • better I/O performance: Each storage in ESX, we only assign to 5 VMs or less. Since more running VMs on a single storage will hit into the LUN I/O speed bottle neck.
  • better disk utilization: You can safe lots of unuse space when you do it small. Say You assign a 2TB storage that can keep 40 VMs, but you only have 20 now, you actually waste 1TB which is sitting there doing nothing. But if you make each storage small, you can create only when you need it. It is much more manageable on SAN disk allocation point of view.

You may ask, if we need a disk in VM that is larger then 256GB? Well, up to that size, you need to consider I/O performance as well, VMFS is just not capable for that size if you are looking for performance as well. Normally we assign a RAW Device for that, you can connect a RAW up to maximum 2TB disk space if required. Check VMware VMFS vs RDM.