Q: What’s the maximum number of disks per SCSI Controller?
A: It depends.. On your VCP exam, you would have said 15. Correct.
Although if you want to clone or snapshot and quiesce a VM, the maximum is 7 disks per SCSI controller.
Each SCSI Controller can control 15 disks and the quiesced snapshots in Windows 2008 require one available slot per existing disk.
If you have more than 7 disks, the clone / quiesce part will fail, and you’ll have the following errors in vCenter and the VM’s vmware.log:
An error occurred while quiescing the virtual machine. See the virtual machine’s event log for details.
2014-12-22T00:19:16.188Z| vmx| ToolsBackup: not enough empty nodes (needed 8, found 7)
2014-12-22T00:19:16.188Z| vmx| ToolsBackup: changing quiesce state: IDLE -> DONE
2014-12-22T00:19:16.188Z| vmx| SnapshotVMXTakeSnapshotComplete done with snapshot ‘clone-temp-1419207556192169’: 0
2014-12-22T00:19:16.188Z| vmx| SnapshotVMXTakeSnapshotComplete: Snapshot 0 failed: Failed to quiesce the virtual machine. (40)
It’s explained in http://kb.vmware.com/kb/2015181.
Just one more way snapshots can bring you pain.
It’s listed as only affecting Windows 2008, but I’m not sure why other versions are exempt. At this time there’s no mention of this affecting vSphere 5.5.
Updated 23/12/2014: This affects Windows 2008 and above (ie: Win 2012), and is still an issue in vSphere 5.5. KB article will be updated.
For the lazy, see here:
Creating a quiesced snapshot of a Windows 2008 virtual machine fails with the error: Snapshot 0 failed: Failed to quiesce the virtual machine. (2015181)