[Xen-users] Re: XEN Images Storage

[Klaus Steinberger <Klaus.Steinberger@xxxxxxxxxxxxxxxxxxxxxx>]

> I want to build on Open Source tools a high availabitiy server to store
> my images, someone with suggestions? experiences plz. really aprreciate.
>
> Started to try Gluster but yesterday discussion pointed me very
> important things.

For Image storage you don't need a Cluster Filesystem. It even maybe a 
performance bottleneck, as any Clusterfilesystem will need write locking over 
the net.

What you really need is some kind of shared storage. That could be 
Fibrechannel, Iscsi or (today not any more common) SCSI.

The shared storage must have redundant paths to be really high availability. 
So that means: Redundant paths to the storage as well as redundant raid 
controllers. (For the FC example:  Dual HBA's, Dual FC Switch, Storage with 
Dual Controller). For the path discovery use dm-multipath.

What I'm doing in the front:

Three server (all with dual FC HBA) with Scientific Linux 5.1 (a RHEL clone 
like CentOS). The servers are members of a cluster (of course you need 
servers with a BMC and IPMI over Lan for the fencing).  On the clusternodes I 
run clvmd (Cluster Logical Volume Manager) and rgmanager (Resource Manager).

The images are just Logical Volumes, they will not be mounted on the hosts. 
The cluster locking is only needed for the lvm commands, so its no 
bottleneck. Any node sees the same images, so on failover another node could 
immediately restart the failed domU.

rgmanager handles nicely the failover of domU's. 

If it's enough availability when you're domU's are up again after a host 
failure after a few 10's of seconds, then that's it.

If you need a little bit more high availability, you could think of clustering 
also domU's and define failover services on that cluster. There are rgmanager 
scripts already in the distribution for a bunch of common services like nfs, 
samba, http and so on.

Any software used in that setup is opensource. You could of course use other 
distributions which support Redhat Clustering, but easiest way is to use 
CentOS or Scientific Linux. Both have long term support and are available 
without license costs.

Sincerly,
Klaus


-- 
Klaus Steinberger         Beschleunigerlaboratorium
Phone: (+49 89)289 14287  Am Coulombwall 6, D-85748 Garching, Germany
FAX:   (+49 89)289 14280  EMail: Klaus.Steinberger@xxxxxxxxxxxxxxxxxxxxxx
URL: http://www.physik.uni-muenchen.de/~Klaus.Steinberger/

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