SR_BACKEND_FAILURE_46 - The VDI is not available


ISSUE: During a backup, you may receive an error

1/18/2017 5:00:52 AM -- Error -- Error attaching disk OpaqueRef:438acdc8-dead-bee4-3594-e5d97bccb35e to VBA: SR_BACKEND_FAILURE_46 

View the XProtect logs in your Unitrends system. If you have a UB or RecoveryOS the path is /usr/bp/logs.dir/. The fix in this case will resolve the following issues found in the logs.

The VDI is not available


RESOLUTION (FIX): Contact your Hardware and/or Storage vendor to ensure you have the latest firmware to meet or exceeds Citrix requirements. Review Citrix KB CTX138234 and consider contacting Citrix to help you reset the VDI if the issue persists.

Things your should try:

  1. Restart the Host where the affected VMs reside on.
  2. Restart the storage container where the affected VMs reside on.
  3. Migrate the VM and its storage to a new host and storage temporarily. (Many users have reported that the migration processes fixes the issue.)
  4. Contact your Host and Storage hardware vendor for the latest firmware updates (verify it is Citrix certified).
  5. Review Citrix KB CTX138234 and consider contacting Citrix. If you need us to help you communicate the issue with Citrix, open a case and provide to use the contact details of your Citrix assigned Engineer so we can setup up a mutual time for working the issue.
If you are still not able to correct this issue, you can still protect your VM by install the Unitrends Client Agent to the affected Guest VM and to protect it using the File Level Protection and if needed Application options.


CAUSE: The message SR_BACKEND_FAILURE_46 is only a designation, (like a light bulb turn on, but not telling you the exact problem). If you look up the error in Citrix KB CTX131215, you find that 46 is an error presenting "The VDI is not available" and this is what the issue is.

This issue occurs when the VM is hard powered down (for example, power loss) which causes storage connectivity issues. The the read / write (RW) lock used to protect the disks from being accessed (for example, by Unitrends) to be stuck making the disk unavailable for reuse or access. The problem lies between the Host and the Storage, preventing Citrix from performing its normal functions.


Please also check on Citrix KB 131215.

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