Re: [Xen-users] xvda vs lvm

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

On Wed, Apr 25, 2007 at 08:18:38AM +0200, tarjei wrote:
> Hi,
> Mark Williamson wrote:
> >>Hi, I'm just wondering if there are any speed or stability differences
> >>between running a system directly of a LVM partition versus a xvd
> >>partition?
> >>
> >>I'm a little confused about what you're asking, so I'll explain a few 
> >>things and hopefully it'll help some.  Please ask again if I'm not 
> >>answering the questions you wanted.
> >>    
> I was mainly wondering about the speed issues involved in the two 
> approaches. Since I didn't hear anything the first few days, I also 
> asked on #xen where I was told that there isn't any performance overhead 
> and that overloading the normal disk, say /dev/hda1, will be phased out 
> in the future.

That doesn't make any sense - the same driver code is used to access both LVM
partitions & regular partitions. LVM does add one extra layer in the kernel
I/O stack compared to directly using regular paritions, but the performance
difference would be pretty small. I can't imagine any difference being a problem
for the vast majority of users, particularly given the flexibilty LVM adds
for management. There are still use cases for regular partitions - eg SAN
where the volume allocation/management is done directly at the SAN rather than
the host thus making LVM less compelling.

Dan.
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