Re: [Xen-users] Looking for tips about Physical Migration on XEN

[tbrown@xxxxxxxxxxxxx]

>
> I don't have URLs or tested environments or performance/speed migration 
> results, but I am planning
> on implementing a similar setup so I can offer tips.

I have done some testing...

> If you still require live migration (as in the case of a game server),
> it seems you must have an external NFS or iSCSI or AoE server.  This is
> because both Xen node servers need to access the storage at the same
> time.  I think AoE is the simplest and best performing, and with the
> vblade daemon it's free and works on any server.  I'd use 2 servers and
> install Heartbeat+DRBD on them for the ultimate in HA.  As an
> alternative you can use shared SCSI storage.

NFS performance sucks. AFAIK, this is because your kernel can't cache
anything... this causes latency on every file open. That said, NFS is
trivial to setup and works fine for live migration (been there).

AoE exports a block device, AFAIK, this means you can _not_ have two nodes
accessing (mounting) it at the same time or you are basically guaranteed
to corrupt either your file system or the kernel's view of it (unless all
mounts are read-only).

Also, at least with the version I tested, the vblade write performance
sucked (5 Mbyte vs 40 Mbyte read) ... and the coraid docs showed similar
numbers 5 Mbyte/s read/write per drive. That may be perfectly acceptable
for you. It isn't bad. I tried nbd and it was much more symetric (40 or
more Mbyte/sec both ways).

That said, I haven't put it all together and into production yet. Going to
have to do that darn soon though.

-Tom


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