[Gluster-users] Block replication with glusterfs for NFS failover

[Runar Ingebrigtsen]

On ti. 23. okt. 2012 kl. 20.33 +0200, Brian Candler wrote:
> On Tue, Oct 23, 2012 at 01:55:01PM +0200, Runar Ingebrigtsen wrote:
>>     to enable NFS state transfer between hosts in a failover SAN, it is
>>     necessary to have the NFS state data on the exact same blocks on both
>>     storage nodes:
>
> You are reading a document for something which is not glusterfs.

I'm sorry - I am aware of that. The part of the document I was meaning 
to reference was the block-by-block replication that was pointed out as 
a requirement for NFS connection handover. I should have pointed out 
what I meant better.

>>     Can I somehow enable block-for-block replication with GlusterFS?
>
> No. You are reading documentation for something completely different: a pair
> of machines synchronised at the block level using DRBD, in a master/slave
> configuration (that is: all writes must be made on the master side, and the
> block changes are replicated a la RAID1 but over a network).

Hm. I don't see how your reply indicates the lack of block-by-block 
replication in GlusterFS.

> I suggest you ask a different question: "can I have failover between two
> gluster NFS servers without getting stale filehandles?"

Good point. I'm happy to annouce that it did turn out that, indeed, you 
can.
The reason it didn't work was a User Error.

When you use UCarp for failover between two GlusterFS servers, the 
Virtual IP address stops responding for about 5 seconds when you unplug 
the UCarp master node. It then takes the NFS client about 45 seconds 
more before it is able to use the GlusterFS/NFS mount on the UCarp 
secondary node.

> I don't know the answer to that myself, but I have seen messages which
> suggests others may have it working:
> http://gluster.org/pipermail/gluster-users/2012-June/010700.html

Thank you.

--
Best Regards
Runar Ingebrigtsen