Wondering how to resolve “SR BACKEND FAILURE 181” error? We can help you.

Here at Bobcares, we often handle requests from our customers to fix similar errors as a part of our Server Management Services.

Today we will see how our support engineers fix this for our customers.

What causes the error “SR BACKEND FAILURE 181”?

Typical error looks like below:

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 resolve “SR BACKEND FAILURE 181” error ?

Today, let us see the steps followed by our Support Techs to resolve the issue.

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

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

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

• 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.

[Still stuck with the error? We can help you]

Conclusion

In short, user experiences issues with any storage related operations after installation or upgrade to XenServer 6.x. Today, we saw the steps followed by our Support Techs to resolve “SR BACKEND FAILURE 181” error.