NFSv4 Active-Active Cluster Queries

[Neil Brown]

On Thursday July 20, urajat at novell.com wrote:
> Hi,
> 
> I have been working on setting up NFSv4 in cluster scenario. But when
> it comes to an Active-Active setup, it seems there are a few problems. 
> 
> In Active-Passive case, the /var/lib/nfs directory itself is moved to
> shared storage & on the nodes in the cluster, symlinks are created
> pointing to the location on shared storage. This isn't possible in case
> of Active-Active setup. In this case, we will need to use scripts to
> merge the information in /var/lib/nfs from the failed node with that on
> the running one and then do a re-export. 
> 
> 1) From the High Availability wiki (http://wiki.linux-ha.org), I got to
> this page -
> http://chilli.linuxmds.com/~mschilli/NFS/active-active-nfs.html where
> a method of setting up Active-Active NFS failover was described.
> Basically a set of scripts is used to duplicate the rmtab entries on the
> node that takes over the process during failover. Will this method hold
> in case of NFSv4 too? What other data would need to be duplicated?

rmtab is simply not an issue - you can ignore it.
Provided /proc/fs/nfsd is mounted, the contents of rmtab are ignored.

What is important is locking state.  For NFSv4, that means the 
contents of /var/lib/nfs/v4recovery.  I don't know exactly how this is
handled.

> 
> 3) Locking issues - revocation & reacquiring of locks.

Wendy Cheng <wcheng at redhat.com> has been looking at what kernel/utils
changes are needed to support this fully, though I think she is only
looking at v3.

> 
> 4) I can see that there is some HA callout code in nfs-utils (under
> support). Is this applicable for NFSv4 also?

No.  Currently all v4 state is handled by the kernel, though that may change.

NeilBrown