VMs that were formerly RDMs (Raw Device Mappings) and which have had one or more disks grown via LUN migrations in EMC Navisphere (or similar functions in another vendor’s SAN tool) may fail to create the appropriately-sized disks on the target SAN during a storage migration. This is due to the fact that the RDM mapping file on the source SAN never updated to reflect the size of the previously grown LUN (via LUN migration). VMware Virtual Center uses that mapping file to create new VMDK files on the target. Thus, if the mapping file is not updated to reflect the proper size, Virtual Center will create a smaller file on the target, possible resulting in loss of data or program integrity.
Example: server1 originally had a 30GB C:\ prior to a rebuild. When it was rebuilt, the same LUNs were used. However, due to a larger RAM allocation (i.e. 8GB instead of 4GB), the C:\ drive needed to be expanded. LUN migration in EMC Navisphere was used to accomplish this. However, the mapping file (the pointer .vmdk file) never changed to the new size. When the migration took place, Virtual Center only created a 30GB virtual disk on the target SAN. Windows booted thinking it had a 50GB disk (the expanded size). The result was that applications (i.e. SQL Server) and possibly other components failed to function after migration.
The solution is to delete and re-add the RDMs of any grown VMs before migration to ensure that the right size is used on the target.
Applies to: VMware ESX 3.x, Virtual Center 2.x