On Mon, 10 Jan 2011 21:21:45 +0100, "Kit Gerrits"
<kitgerrits@xxxxxxxxx> wrote:
Hello fellow administrator,
If you have a SAN...
Why can't you have the SAN publish the same LUN to the two cluster
nodes
simultaneously?
You can, but you minimally need to guarantee (not believe or think, but
guarantee!) that both nodes do not
a) write to the same sectors, file systems or LVM volumes at the same
time (this is actually a whole lot more difficult to do than most people
think) - including boot sectors, partition tables, LVM metadata, etc,
etc,
b) think they're exclusively accessing the LUN I.e. there must be
something on the nodes - an application, OS tool or something else -
that understands that there is more than one reader & writer to a LUN
and thus synchronizes this.
It is only used as a raw device, so there should be no ugly
filesystem
side-effects.
File systems only serve to make this a lot more obvious to the end user
or administrator since it's integrity tends to get shot fairly quickly
and there are integrity checks in place. On raw devices, you get the
"benefit" of ignorance about the fact that your data is corrupt, unless
b) above is true.
Hth,
// Thomas
Regards,
Kit
-----Original Message-----
From: linux-cluster-bounces@xxxxxxxxxx
[mailto:linux-cluster-bounces@xxxxxxxxxx] On Behalf Of Andreas
Bleischwitz
Sent: maandag 10 januari 2011 11:25
To: linux-cluster@xxxxxxxxxx
Subject: Howto define two-node cluster in
enterpriseenvironment
Hello list,
I recently ran into some questions regarding a two-node cluster in an
enterprise environment, where single-point-of-failures were tried to
be
eliminated whenever possible.
The situation is the following:
Two-node cluster, SAN-based shared storage - multipathed; host-based
mirrored, bonded NICS, Quorum device as tie-breaker.
Problem:
The quorum device is the single-point-of-failure as the SAN-device
could
fail and hence the quorum-disc wouldn't be accessible.
The quorum-disc can't be host-based mirrored, as this would require
cmirror
- which depends on a quorate cluster.
One solution: use storage-based mirroring - with extra costs, limited
to no
support with mixed storage vendors.
Another solution: Use a third - no service - node which has to have
the same
SAN-connections as the other two nodes out of cluster reasons. This
node
will idle most of the time and therefore be very uneconomic.
How are such situations usually solved using RHCS? There must be a
way of
configuring a two-nodecluster without having a SPOF defined.
HP had a quorum-host with their no longer maintained Service Guard,
which
could do quorum for more than on cluster at once.
Any suggestions appreciated.
Best regrads,
Andreas Bleischwitz
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