If you have ever had to reattach a disconnected SR to your XenServer (I published a blog post with instructions on how to do this some time ago), you will be already familiar with the xe-pbd-plug command.

Sometimes this command will not complete successfully, and you might get the following error code:

SR_BACKEND_FAILURE_52

and/or
[ ; Logical Volume mount/activate error [opterr=FSCK failed on
/dev/XSLocalEXT-your-uuid. Errno is 8]; ]")

I have had this happen to me on my EXT drives sometimes, and the solution is simple: just wait for a couple of minutes and run the xe-pbd-plug command again.

In my experience, when I see SR_BACKEND_FAILURE_52 together with a Logical Volume mount/activate error mentioning FSCK and Errno 8, I just have to give some time to the system before running xe-pbd-plug. No idea why this is the case, but it seems to work every time I run into this.