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Re: [Xen-users] XEN and clustering?

Steven Wilcoxon wrote:
I would think running LVM in Dom0 instead of DomU gains you performance by using Dom0's CPU & disk cache instead of taking it out of the DomU resources.

First off, the overhead of LVM in i/o and such is likely a small percentage of the i/o of Xen itself, which we all know to be very small. In other words, its overhead is negligible no matter where it's run.

Second, I don't know what you're referring to here with cpu and disk cache, especially with regard to disk cache, as LVM does little or none as far as I know. I run my dom0's with a hard-coded 512MB so I don't have any cache there anyway, but I'm running LVM on top of LVM (phy: mappings of lv's) so cache is irrelevant). Unless you're using tap:aio, if you're going to use cache, it's in the domU.

Third, if there is some resource utilization going on specific to a domU, I'd rather have that happen in the domU where it has minimal impact on other domU's rather than in dom0 where it affects them all. There are exceptions: you don't want things that have to cross the hypervisor twice to exist in domU like RAID and multipathing.


John Madden
Sr UNIX Systems Engineer
Ivy Tech Community College of Indiana

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