[DRBD-user] DRBD + NFS

[Dan Brown]

On Saturday, October 14, 2006 Mustafa A. Hashmi wrote:
> On 10/10/06, Dan Brown <danb at zu.com> wrote:
> >
> > So while server A is the active NFS server and server B is 
> passive and 
> > only synching, both servers would mount via NFS server A.  
> When server 
> > A goes down for whatever reason (reboot, crash, etc) server 
> B will take over and
> > continue where server A left off.   One thing I keep seeing 
> in various
> > documents however is a warning not to have the server mount its own 
> > NFS shares.  There is never reason (even a vague reason) 
> given why not 
> > to however.  I can see the obvious reasons (eg. infinitely nested 
> > filesystems via symlinks/mounts, crossmounts, etc), but my 
> directory structures should
> > not need anything like this at all.   Other than overall 
> system complexity,
> > I don't see any reasons to not be able to self mount NFS 
> with a whole 
> > lot of trouble.
> 
> Odd -- the NFS-HA howto shows how to do exactly this. Also: 
> we've deployed this for mail and web without issues this far, 
> albeit, in a non-complex environment.

You mean the one at http://linux-ha.org/HaNFS ?  It examples a setup with to
HA NFS servers, and two clients (although not specifiying whether they are
one in the same) . This, along with a fair number of other articles I've
read on using DRBD and NFS all have something like this (from the
linux-ha.org page): 

"NFS-mounting any filesystem on your NFS servers is highly discouraged."

But none of them ever really give a good explanation(if at all)  why.
Having not done much with NFS before, and certainly not in a production
environment, I don't have the experience with NFS to understand many reasons
behind this sort of statement. 


__________________________________________________________
Dan Brown
danb at zu.com