[Gluster-users] NFS availability

[Stephan von Krawczynski]

On Thu, 31 Jan 2013 09:07:50 -0800
Joe Julian <joe at julianfamily.org> wrote:

> On 01/31/2013 08:38 AM, Stephan von Krawczynski wrote:
> > On Thu, 31 Jan 2013 12:47:30 +0000
> > Brian Candler <B.Candler at pobox.com> wrote:
> >
> >> On Thu, Jan 31, 2013 at 09:18:26AM +0100, Stephan von Krawczynski wrote:
> >>>> The client will still fail (in most cases) since host1 (if I follow you) is
> >>>> part of the gluster groupset. Certainly if it's a distributed-only, maybe not
> >>>> if it's a dist/repl gluster.  But if host1 goes down, the client will not be
> >>>> able to find a gluster vol to mount.
> >>> For sure it will not fail if replication is used.
> >> Aside: it will *fail* if the client reboots, and /etc/fstab has
> >> server1:/volname, and server1 is the one which failed.
> > Well, this is exactly the reason we generally deny to fetch the volfile from
> > the server. This whole idea is obvious nonsense for exactly the reason you
> > described.
> >
> That doesn't lend me much confidence in your expertise with regard to 
> your other recommendations, Stephan.
> 
> There are two good ways to make this work even if a server is down:
> 
>   * Round robin DNS. A hostname (ie. glusterfs.domain.dom) with multiple
>     A records that point to all your servers. Using that hostname in
>     fstab will allow the client to roll over to the additional servers
>     in the event the first one it gets is not available (ie.
>     "glusterfs.domain.dom:myvol /mnt/myvol glusterfs defaults 0 0").

You don't want to use DNS in an environment where security is your first rule.
If your DNS drops dead your setup is dead. Not very promising ...
The basic goal of glusterfs has been to secure data by replicating it.
Data distribution is really not interesting for us. Now you say "go and
replicate your data for security, but use DNS to secure your setup".
???
You really seem to like Domino-setups. DNS dead => everything dead.

>   * The mount option backupvolfile-server. An fstab entry like
>     "server1:myvol /mnt/myvol glusterfs backupvolfile-server=server2 0
>     0" will allow the mount command to try server2 if server1 does not
>     mount successfully.

And how many backup servers do you want to name in your fstab? In fact you
have to name all your servers because else there will always be at least one
situation you are busted. 
 
> This whole idea is obvious experience and forethought, not nonsense. By 
> having a management service that provides configuration, on-the-fly 
> configuration changes are possible. If one "denies to fetch the volfile" 
> one cripples their cluster's flexibility.

I don't know what kind of setups you drive. In our environment we don't want
to fiddle around with fs configs. We want them to work as expected even if
other parts of the total setup fall apart. Flexibility in our world means you
can do widespread types of configurations. It does not mean we switch the
running configs every day only because gluster is so flexible.

-- 
Regards,
Stephan