@dthenot ... The XOSTOR SR is working on the other hosts. It's only the master which updated where it fails to plug the pbd. Given that it can't mount the pbd after doing the update, I am very doubtful about updating another host.
What's more, I can't without shutting down a large number of VMs or doing a long migration off the XOSTOR, because I only have N+1 redundancy on my personal cluster, and we're already one host down because the master can't rejoin the XOSTOR SR.
In short, this looks like a very dangerous suggestion - sorry!