I just finished migrating a VM from a host running ESXi 4 to ESXI 5.1U2, after upgrading the virtual hardware from 7 to 9 I find that the hard disk is now IDE when it was SCSI, why did this change? My problem now is that I need to expand the size of the single disk on the VM and its not an option since the disk is now IDE instead of SCSI. I expanded the disk a few months ago when it was on the old host, its size is now 60GB, I had added 10GB to it before. I have checked a few other VM's that I have migrated from the same host running ESXi 4 to this host and their disks are still SCSI. How can I resolve this so I can expand the disk?
Never seen this happen but check this blog to know how to change from IDE to SCSI: http://www.jjclements.co.uk/2010/06/08/vsphere-convert-vm-ide-disk-to-scsi-disk/
I'm not sure why the controller went from IDE to SCSI on you on that particular VM??? However with an IDE controller you can't expand the disk, so until you move it back to SCSI you won't be able to expand it again. With that said you have a few options. One is clone the system and on the clone try and do a direct replacement of the controller. Since the OS had the SCSI controller previously it will probably handle the switch okay without any boot issues or BSOD, however I would try this on a clone first before the production system.
The other option is you can P2V the VM and switch the controller that way We had to do this to one of our production VMs not that long ago as when it was originally P2V'ed it was from an OLD physical server that had an IDE system in it so the P2V process selected IDE.
Hope this has helped.
You will have to convert the disk back to SCSI.
This will help you with that http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=101619...
Once you are done, you will be able to expand the disk.