How to change the blocksize of a VMFS filesystem

By default, VMWare ESX server uses a 1M block size which limits you to having a maximum of 256GB in any single virtual machine.  By changing the block size of your vmfs partition, you can increase the maximum amount of disk you can have.  A 2M block size yields a maximum disk size of 512 GB, 4M yields 1TB, and 8M yields 2TB.  There is no support for anything larger under vmfs3.  Vmfs2 had a maximum block size of 16M, but that has been removed in the vmfs3 specification.

To change the block size of a vmfs filesystem, you need to use vmkfstools to reformat the partition.  The command is:vmkfstools --createfs vmfs3 --blocksize 8M vmhba0:0:0:3 It is important to note that like any other formatting procedure, this will destroy any data on the partition, so make sure you move your data before you do this.  The “vmhba0:0:0:3″ is where you specify which partition to reformat.  According to the VMWare server configuration guide, the format is:

vmhbaA:T:L:P format, where A, T, L, and P are integers representing adapter, target, LUN, and partition number respectively. The partition digit must be greater than zero and should correspond to a valid VMFS partition of type fb

For example, vmhba0:2:3:1 refers to the first partition on LUN 3, target 2, HBA 0.

If you’re reformatting a current vmfs filesystem just to increase the blocksize, you can get that information from the storage section in the configuration tab of the Virtual Infrastructure Client.