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Re: [Xen-users] very slow disk access

On Sun, Feb 27, 2011 at 9:11 AM, Randy Katz <rkatz@xxxxxxxxxxxxxxxxxxxxx> wrote:
> it seems I am using tap:aio on what appears to be quite slow:
> disk = [ "tap:aio:/disk0/server3.img,xvda,w" ]
> Is there a good way to convert from tap:aio to lvm? I tried stop vm, dd
> if=server3.img of=/dev/vg1/newlv3
> but it is very very slow, much quicker to blow away the whole thing (vm) and
> reinstall and then add data
> from backups.

dd is the generic way. You might want to use dd_rescue (available as
rpm from EPEL), which should at least show you what it's doing and how
fast it's doing it. 6 - 10MBps is quite normal if you only have one

If your image is still empty-ish (e.g 20GB file image with only 2GB
used), it might be faster to copy MBR first (which includes partition
table), setup your system so you could access the partition on LVM
(using something like kpartx), and use something like partclone or
clone2fs to copy only used blocks.


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