[wplug] NFS Availability Issues -- Linux HA for web (even NFS shared web data) v. traditional NFS home dirs

[Brandon Poyner]

On 9/12/07, Bryan J. Smith <thebs413 at yahoo.com> wrote:

> There are just some aspects where NFS really doesn't work with the
> DRBD + Linux HA approach.  Beyond the fact that NFS wasn't designed
> for it at all, the majority of people I've seen using this
> configuration are using it, again, for web.  The web servers are not
> only tuned into the Linux HA part, but they are _not_ "keeping files
> open."

NFS certainly brings its own baggage, and I'll say that I personally
don't use DRBD + HA for any type of NFS services.  In fact I'm not a
huge fan of NFS partially because it's not 'designed for' high
availability.  I've been using DRBD for web, mail, smtp, lpd, etc
without any type of file open/locking issues.

But that doesn't mean that some people haven't had good success with
DRBD + HA + NFS.  Keep in mind that this is trying to do something at
a very low capital expenditure.  If you have the money to spend on
something better by all means use something better.

The HA wiki addresses NFS file locking with the following two disclaimers:

If client applications do not use file locking, HA NFS works very
well. However, if a client application uses locking, it may get errors
that it will not get in a single NFS server. IMHO there are some bugs
in NFS that cause problems above. -- GuochunShi

However, most of these are now fixed, if you're running the right NFS
kernel. But, the occasional lock failure in intensive locking can
still occur. There is not yet any known solution. -- AlanRobertson

Source:  http://www.linux-ha.org/HaNFS

If I were attempting to make a highly available networked filesystem
on the cheap, I would probably go with DRBD with a clustered
filesystem and skip NFS altogether.  The Xen community, another big
group using DRBD in interesting ways, has reported success with that
method.

-- 
Brandon
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