Re: [Xen-users] XEN and clustering?

[John Madden <jmadden@xxxxxxxxxxx>]

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




--
John Madden
Sr UNIX Systems Engineer
Ivy Tech Community College of Indiana
jmadden@xxxxxxxxxxx

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