Cluster, shared LUN, and multi-host filesystems
hume.sp...@bofh.ca
building. It'd be nice to have the mail store shared, with multiple
IMAP front-ends for the users to interact with. An NFS backend is one
possibility, but another thing I was thinking of was multiple IMAP
machines sharing a LUN from the SAN.
I've found some comments online that this would be possible with some
Solaris machines running Sun Cluster. Including, even, that it could be
done with metasets and UFS. But not so much any actual how-tos or details.
If I had some more spare machines here, I'd simply try it and see, but I
don't at the moment. But before I chase this too far, has anyone even
heard of something like this?
I'd be looking at a few machines clusters, sharing a LUN, hopefully serving
data with Cyrus IMAP.
--
Brandon Hume - hume -> BOFH.Ca, http://WWW.BOFH.Ca/
Gary Mills
>I've found some comments online that this would be possible with some
>Solaris machines running Sun Cluster. Including, even, that it could be
>done with metasets and UFS. But not so much any actual how-tos or details.
I started on the same project, but ran out of time and had to go
with a single T2000 server instead of two nodes in a cluster.
>I'd be looking at a few machines clusters, sharing a LUN, hopefully serving
>data with Cyrus IMAP.
I was using Iscsi LUNs on the two nodes. At the time, Sun Cluster
didn't support Iscsi. I assume it does now. In any case, you will
need a cluster filesystem if you want both nodes active at the same
time. We also wanted snapshots, which made the whole thing more
difficult.
Check the Cyrus archives. I believe that at least one Cyrus cluster
has already been built.
--
-Gary Mills- -Unix Support- -U of M Academic Computing and Networking-
Wolfgang
> I'm investigating some options for a new IMAP cluster we're thinking of
> building. It'd be nice to have the mail store shared, with multiple
> IMAP front-ends for the users to interact with. An NFS backend is one
> possibility, but another thing I was thinking of was multiple IMAP
> machines sharing a LUN from the SAN.
with a NFS backend you have the same problem with that: it is just a
single server until you build it clustered.
>
> I've found some comments online that this would be possible with some
> Solaris machines running Sun Cluster. Including, even, that it could be
> done with metasets and UFS. But not so much any actual how-tos or details.
metasets can be used to fail over a SAN Storage, it has no Cluster
Filesystem buildin, the Sun Cluster add this by QFS. metasets can
imported only on one machine, same as in Veritas VM without CFS.
dont try to access pure SAN disks from more than one system concurrent,
especially writes ;-)
Nevertheless: You need a cluster file system (Veritas CFS, GPFS, QFS),
hopefully sun integrates ClusterFS ZFS, but it seems not.
Since SunCluster is now for open use that on solaris. maybe symantec
have a free cluster with limitations (but I dont think for sparc).
Alternatively an clustered applikation can do the work, e.g. a imap
frontend working on a replicated mysql database, but i dont now about one.
Another solution would be to spread the users over several servers,
maybe the easiest way to do a sort of loadbalancing. user a*-d* on
server a, e-h on server b and so on.
if you want only HA: have a look for pen, plb or similar or build a poor
mans cluster with rsync and and vrrpd (or sun cluster ;-).
W.
Frank Fegert
Take a look at:
http://docs.sun.com/app/docs/prod/sun.cluster32
Especially:
http://docs.sun.com/app/docs/doc/819-2969
http://docs.sun.com/app/docs/doc/819-2968
for the terminology and concepts, and:
http://docs.sun.com/app/docs/doc/819-2970
http://docs.sun.com/app/docs/doc/819-2971
for Cluster install and administration.
The CFS provided by Sun/Solaris Cluster is not a true multiple reader/
writer FS like e.g. Sun QFS, it's rather an additional VFS-layer adding
similar capabilities to non-CFS filesystems like UFS. The reads/writes
from the cluster nodes are proxied via the cluster interconnect to the
cluster node owning the disk group and performing the actual read/write
from/to the disk group. Inherently this will be slower than direct access
on the same hardware. If you're just looking for HA, CFS might suffice.
If you're looking for high performance and you can afford it, Sun QFS
or Veritas CFS may be a better choice.
HTH,
Frank