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Re: [Xen-users] IO is a big difference between the "file" and "phy"

On Wed, Jun 13, 2012 at 11:00 AM, ÐÑÑÐÐÐ ÐÐÑÐÐÐÐ <ufaweb@xxxxxxxxx> wrote:

> Here, /dev/nas-1/mogilefs-images is logical volume in LVM, /mnt/ext4
> is file located on the other logical volume in the same LVM.
> LVM is one volume group located on one physical volume (software raid6
> - 12 hdd).

> Why such a big difference in the rate of io (is physically on the same 
> device)?

That's a known issue.

Depending on your configuration, dom0 kernel version, and type of
test, file:/ can be MUCH faster, or MUCH slower compared to phy:/, due
to interaction of dom0 filesystem, loopback driver, and dom0 kernel
cache.  But it shouldn't matter in production environment, as you're
NOT supposed to use file:/ anyway, since (on some circumstances) it
can cause data corruption.


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