[Linux-HA] HB general question

[Slawomir Mroczek]

On Wed, 13 Dec 2006 16:43:58 +0100
MIQUET Pascal <pascal.miquet at wanadoo.fr> wrote:

> Thanks for your reply.
> 
> The main question is that both servers will do some specific stuff, I
> mean a server will run jobs on primary and secondary.

And that's OK. I didn't say that secondary server has to be idle.

> We do not have GFS, but the same storage could be mounted on each
> servers but there is no concurrent access, this is why we start with a
> NFS mounted file system. As the secondary is not very loaded, I've
> started the NFS export on this server.

NFS is not a bad choise, however when you use shared storage it's the
shame not to use some cluster filesystem, becouse there is a risk of
filesystem corruption with cluster split-brain when both nodes write
to the same mounted block device. In this case you HAVE TO take care
about STONITH, also. Hovever when you want to have "symmertic" cluster
resources a cluster FS is what you really want to run.

> But as I see with HeartBeat, services will run on the primary, so I
> need to use a specific script to mount and then export the file
> system on the VIP server.
> 
> Is GFS free ?

No. You have to pay for support. And you have to know, that GFS requires
a HA cluster to work, so Red Hat Cluster Suite is included with Red Hat
GFS. As you can see with ttis solution you can have cluster filesystem
and High-Availability cluster. BUT...! GFS is open source (so is RHCS),
so in my opinion you can install it "for free" once you download it.
Second "BUT!": GFS (and RHCS) for RHEL3 is rather old. In fact RHEL3 is
old, too. In my opinion you should upgrade to RHEL4. And in my opinion
you should REALLY consider switching to Novell's SUSE Linux Enterprise
Server. At least version 9 with SP3. SLES9 (and SLES10) has Heartbeat
included and it has Oracle Cluster Filesystem ver2 included also
(http://oss.oracle.com/projects/ocfs2/). As you can see with SLES you
can build fully functional clusters. I've build solutions based on
RHEL and SLES and in my opinion RHEL4 is far behind SLES9/SLES10.
SLES is really enterprise distribution while RHEL is only a stable
version of Fedora and to gain enterprise functionality you have to pay
horrible amount of money. Look at the RHEL4 AS - it is RHEL4 ES with
extended support, but it is THE SAME distro with /etc/redhat-release
changed. If you really love RHEL you should better go to CentOS - it is
"free" RHEL. 

> Does it share the file system with some concurrent access ?

It is cluster filesystem. This allows the cluster nodes to
simultaneously read and write to a single shared filesystem and provide
a consistent file system image across the server nodes.
http://www.redhat.com/whitepapers/rha/gfs/GFS_INS0032US.pdf

-- 
Slawomir Mroczek