Maximum Disks Per SCSI Controller is NOT 15

calendar Dec 22, 2014 · 3 min read  ·
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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.

CREATING A QUIESCED SNAPSHOT OF A WINDOWS 2008 VIRTUAL MACHINE FAILS WITH THE ERROR: SNAPSHOT 0 FAILED: FAILED TO QUIESCE THE VIRTUAL MACHINE. (2015181)

Symptoms

  • Cannot create a quiesced snapshot of a Windows 2008 virtual machine.
  • Creating a quiesced snapshot of a Windows 2008 virtual machine fails.
  • In the vmware.log file of the affected virtual machine, you see entries like this:
```
XXXX-03-08T04:10:09.790Z| vmx| SnapshotVMXTakeSnapshotComplete done with snapshot 'test4': 0
XXXX-03-08T04:10:09.790Z| vmx| SnapshotVMXTakeSnapshotComplete: Snapshot 0 failed: Failed to quiesce the virtual machine. (40).
XXXX-07-01T15:30:43.244Z| vmx| ToolsBackup: not enough empty nodes (needed 9, found 6)
```

where the values provided in the errors can vary.

Cause

Each SCSI Controller can control 15 disks and the quiesced snapshots in Windows 2008 require one available slot per existing disk. This issue occurs if the virtual machine has more than seven disks attached to a single controller.

Resolution

To resolve this issue:

  1. Create a new thin virtual disk. This allows you to add a new SCSI Controller.
  2. Ensure the new thin virtual disk is attached to SCSI1:0 node.
  3. Retry creating the quiesced snapshot. You are now able to create the snapshot successfully.

Alternatively, for virtual machines with more than 7 disks on a single SCSI controller, instead of creating a new thin disk and adding this to a new SCSI controller (SCSI1:0):

  1. Shut down the virtual machine.
  2. Spread out the existing disks between multiple SCSI controllers. To do this:
  3. Right-click the virtual machine and click Edit Settings.
  4. Change the Virtual Device Node to your new desired SCSI controller.
  5. Power on the virtual machine.

Note: Use this method if there is limited storage space or limited authority to create new disks.