In order to be able to server files over multiple protocols like SMB(2) / NFSv4, on active/active clusters (using CTDB for example), it is necessary to have support for cluster wide leases so that oplocks/delegations can be granted to clients. Without gfs2 support you can't correctly grant oplocks/delegations to clients without risking file corruption.
Created attachment 414191 [details] Old rhel4 patches to implement cluster-leases I wrote this patchset for rhel4 gfs way back in 2006. I'm just posting it here so we can borrow ideas from it if necessary. From what I remember about this, there were multiple glocks per inode to be held during open/close and this introduced a fair amount of overhead. We shelved the patchset due to this overhead and also because not many people (except samba) were wanting to use it.