[Linux-cluster] High Availability options

[Andreas Laumann]

Am Donnerstag, den 13.07.2006, 14:45 -0500 schrieb Stephen Kirkpatrick:
> Lon Hohberger wrote:
> > On Thu, 2006-07-13 at 12:14 -0500, Stephen Kirkpatrick wrote:
> >
> >   
> >> Thanks for the reply.  I wondered if it was possible to have HA for 
> >> stateful applications.  At least
> >> I know my options better now.  I can tolerate brief downtime, like the 
> >> time it would take a failover
> >> node to take over, although no downtime would have been preferred.
> >>
> >> Any suggestions on HA solutions for a non-SAN deployment?
> >>     
> >
> > You don't need a SAN if you don't intend to share data.  
> >
> > If you intend to share data but do not want a SAN, you'll need to set up
> > DRBD or CLVM+Cluster Mirroring+GNBD (Note: cluster mirroring is still in
> > a bit of development).  The main advantage to the latter approach is
> > simultaneous read/write access from both machines in the cluster.  The
> > advantage to DRBD is that it is easier to set up.
> >
> > Alternatively, you could use NFS mounts from a good NAS (a NetApp filer,
> > as an example) as your source for shared dat.
> >
> > You can use linux-cluster or Linux-HA to do failover with or without a
> > SAN; the choice is up to you.  Linux-HA supports DRBD out of the box,
> > but CLVM will still need parts of linux-cluster running in order to
> > operate.
> >
> > If you want support, you can use Red Hat Cluster Suite (which is
> > effectively linux-cluster w/ support).
> >
> > Good luck!
> >
> > -- Lon
> >
> > --
> > Linux-cluster mailing list
> > Linux-cluster at redhat.com
> > https://www.redhat.com/mailman/listinfo/linux-cluster
> >
> >
> >   
> Thanks for the info.  If I understood correctly what I was reading
> about DRDB, it sounds like it runs entirely over an IP network.
> This sounds like what I had originally envisioned for this project,
> as it is a small deployment.
> 
> I was envisioning SCSI storage in two nodes with individual
> internal RAID arrays as depicted in the diagram below,
> 
> 
> +----------------+          +------------------+
> | Primary server |            | Secondary server |
> |                |            |                  |
> |  -----------   |/          \|   -----------    |
> |     RAID-1     |------------|      RAID-1      |
> |  -----------   |\    |     /|   -----------    |
> |                |     |      |                  |
> +----------------+     |      +------------------+
>                        |
>                        +-- Data sync over IP network?
> 

Yes, Data is synced by DRBD via the IP network.

> 
> I was thinking fibre channel storage when I said no SAN.  The
> cost of deploying fibre storage is a bit much for this small
> project.  However, if there is a good way to utilize shared
> SCSI storage and a good HA solution to go along, I would be open
> to researching it.
> 
> In your response, you indicated that Linux-HA supports DRDB out
> of the box.  Does the Red Hat Cluster Suite support this too?
> The Cluster Project FAQ just mentions the CLVM/GNBD solution.

Hi Stephen,

We've build a very similar HA Cluster with multiple network RAID1 block
devices some month ago with RHES 4U3 / RHCS 6.1 and DRBD.  After some
fight with the start scripts of RHCS we're now in production with a
postgresql DB, some application servers and also a huge NFS share
exported to a front end RHCS cluster. All the 'services' use its own
block devices  mirrored by DRBD to a second machine. 

Till now everything is running very well and speedy.
There is only one thing to mention, if you have multiple DRBD block
devices to replicate you should have different mirror groups for the
replication in the DRBD config. Otherwise it is very easy to saturate
even a gig eth.


Greetings
	Andreas


> 
> Thanks,
> Stephen Kirkpatrick
> 
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