After installation or upgrade to XenServer 6.0, user experiences issues with any storage related operations. The following error message appears:
“SR_BACKEND_FAILURE_181 Error In metadata Volume Operation For SR.”

The following entries appears in the log /var/log/SMlog file:

Error code: SR_BACKEND_FAILURE_181
Error parameters: , Error in Metadata volume operation for SR. opterr=VDI delete operation failed for parameters: /dev/VG_XenStorage-427796a3-6891-dcb7-681f-cc7c5463ea0a/MGT, 7b496cd3-9d9c-4cb4-b510-4613e65e7141. Error: not well-formed (invalid token): line 1, column 99,
[10146] 2011-11-27 08:05:10.977985 Raising exception [181, Error in Metadata volume operation for SR. [opterr=VDI delete operation failed for parameters: /dev/VG_XenStorage-511f729e-0f0e-a679-9b8e-4d7ed28f6537/MGT, 65f8e675-9416-4909-8cd1-b7d75af06762. Error: not well-formed (invalid token): line 1, column 65]]
[10146] 2011-11-27 08:05:10.978109 lock: released /var/lock/sm/511f729e-0f0e-a679-9b8e-4d7ed28f6537/sr [10146] 2011-11-27 08:05:10.979583 ***** sr_scan: EXCEPTION SR.SROSError, Error in Metadata volume operation for SR. [opterr=VDI delete operation failed for parameters: /dev/VG_XenStorage-511f729e-0f0e-a679-9b8e-4d7ed28f6537/MGT, 65f8e675-9416-4909-8cd1-b7d75af06762. Error: not well-formed (invalid token): line 1, column 65]

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As a workaround, you can remove all special characters from the virtual machine name-label and description fields.  Contact Citrix Technical Support to assist you in resolving the issue. 
Note: Special character should not be used for the storage repository and description field.

In situation where the preceding workaround is unsuccessful, rebuild the SR MGT volume after removing the special characters:

1. Run lvscan and search for the MGT volume for the respective Storage Repository (SR).
   Example: ACTIVE '/dev/VG_XenStorage-c14bee2a-44da-656a-5b99-865818c0a700/MGT' [4.00 MB] inherit

2. Run a test to verify that the lv can be renamed:
   lvrename -t /dev/VG_Xenstorage- <SR-uuid>/MGT /dev/VG_Xenstorage- <SR-uuid>/MGT.bak

3. When the preceding test is successful, run lvrename without the “-t” option:
   lvrename /dev/VG_Xenstorage- <SR-uuid>/MGT /dev/VG_Xenstorage-< SR-uuid>/MGT.bak

4. Restart the master host in the pool or unplug and re-plug the Physical Block Device (PBD) on the Master Host for the respective SR to build a new MGT volume.
   Example:
   Find the Master Host UUID > xe pool-list params=master
   master ( RO)    : 9079cff1-c457-4e51-b924-8a9e1ec24179

5. To find the master PBD, run > xe pbd-list sr-uuid= c14bee2a-44da-656a-5b99-865818c0a700 host-uuid=9079cff1-c457-4e51-b924-8a9e1ec24179
   uuid ( RO) : 99c6d7ec-75ef-1071-d925-5ff6b4667ecc
   host-uuid ( RO): 9079cff1-c457-4e51-b924-8a9e1ec24179
   sr-uuid ( RO): 20daa9a1-a9b2-ddc9-30a7-c4e15999a284
   device-config (MRO): device: /dev/sdb
   currently-attached ( RO): true

6. Unplug the PBD for the master (using the PBD UUID from Step 5):
   xe pbd-unplug uuid=99c6d7ec-75ef-1071-d925-5ff6b4667ecc

7. Re-Plug the PBD to attach the host to the SR again:
   xe pbd-plug uuid=99c6d7ec-75ef-1071-d925-5ff6b4667ecc

This process will rebuild the MGT volume with the updated information without the special characters in the virtual machine name or description that was previously causing the errors.

Solution

Refer to the following Knowledge Center articles for the current updates that address this issue as of 01/02/2013:
CTX135411 - Hotfix XS60E022 - For XenServer 6.0
CTX135623 - Hotfix XS602E013 - For XenServer 6.0.2

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Problem Cause

XenServer does not properly store the incoming virtual machine name-label and description fields in management VDI (MGT).

Error: SR_BACKEND_FAILURE_181 Error In metadata Volume Operation For SR.