"SR BACKEND FAILURE 181" error - Fix it Now ?








"SR BACKEND FAILURE 181" error happens when XenServer does not properly store the incoming virtual machine name-label and description fields in management VDI (MGT).

Here at Ibmi Media, as part of our Server Management Services, we regularly help our Customers to perform related Server Monitoring queries.


What triggers the error "SR BACKEND FAILURE 181" ?

After installation or upgrade to XenServer 6.x, user experiences issues with any storage related operations.

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]


How to fix the error "SR BACKEND FAILURE 181" ?

First and foremost, you can remove all special characters from the virtual machine name-label and description fields.

If the above workaround is unsuccessful, rebuild the SR MGT volume after removing the special characters:

1.Firstly, 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. Then, 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. Then, 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

i. Unplug the PBD for the master (using the PBD UUID from Step 5):

xe pbd-unplug uuid=99c6d7ec-75ef-1071-d925-5ff6b4667ecc

ii. 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.


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Conclusion

This article covers how to fix "SR BACKEND FAILURE 181" error. Generally, user experiences issues with any storage related operations after installation or upgrade to XenServer 6.x. 

As a workaround, you can remove all special characters from the virtual machine name-label and description fields.  Contact our Technical Support to assist you in resolving the issue. 

Note: Special character should not be used for the storage repository and description field.


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