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Re: [Xen-users] RAID-1 strategy for a Xen/CentOS server?

To: "Tom Brown" <xensource.com@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] RAID-1 strategy for a Xen/CentOS server?
From: "Bob Tomkins" <bob.r350@xxxxxxxxx>
Date: Fri, 7 Dec 2007 11:42:24 -0800
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Hi Tom,

because vbd are slower than "real-world" devices, I believe you want to
move the mirroring into dom0, so that the domU's aren't sending the same
data through the hypervisor twice... beyond that, all the rules are the
same as they would be in a non-XEN config. (This just makes plain sense,
there's less work to be done.)

There may be situations where it makes more sense to do the raid in the
domUs, but you listed "optimize performance".

Thanks for the reply.

Yes, performance is my primary concern, at least during my planning.  (One DomU
 will consist of Zimbra/CentOS, which I understand to be an I/O hog, so I'm trying to remove what bottlenecks I can> It still remains to be seen, but Zimbra *itself* may be on eo fthose bottleneck that gets removed.)

As for moving the mirroring into DomU, generally, I've been slowly coming to the same conclusion.

Am I correct in my understanding that each DomU contains an instance of OS/kernel + app binaries in it's own virtual volume/file space, but that *data* (effectively, *any* dynamic content) is written by the DomU processes to/from the Dom0 hypervisor's volume/file space?

How about swap?  Dom0 of course has its swap -- and could/should be RAIDed, but what about  GuestOS' swap?  I honestly haven't gotten that far yet ....

And, if DomU hosts the RAID mirror, what's the recommended file system choice -- or is that dicated by Xen as a preference (I haven't got to that either yet ...)


Bob Tompkins
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