[fedora-virt] porting a disk from lvm to file

[Avi Kivity]

  On 08/22/2010 10:02 PM, Richard W.M. Jones wrote:
>
>> Interesting, I'd have guessed that encryption will dominate the cpu
>> cost, and that compression would be a win since there's less to
>> encrypt and transmit.
> Maybe my explanation is wrong too.  virt-p2v was definitely much
> slower when we added the '-C' option.  However read on.
>
> I just ran a test again on my local LAN.  This is between two
> approximately equal Fedora machines, over a moderate quality consumer
> gigabit ethernet switch.  The command approximates what virt-p2v does:
> sending 1MB blocks from local /dev device, and at the target end using
> cat to write to a file.
>
> $ time sh -c 'dd bs=1M if=/dev/vg_trick/Windows7x64 | ssh amd "cat>  /tmp/copy1"'
> 16384+0 records in
> 16384+0 records out
> 17179869184 bytes (17 GB) copied, 1473.26 s, 11.7 MB/s
>
> real	    24m33.269s
> user	    4m16.944s
> sys	    4m43.181s

11.7 MB/s = 93.6 Mb/s.  Not the cpu is not loaded.  Are you sure you're 
using 1GbE here?

> $ time sh -c 'dd bs=1M if=/dev/vg_trick/Windows7x64 | ssh -C amd "cat>  /tmp/copy2"'
> 16384+0 records in
> 16384+0 records out
> 17179869184 bytes (17 GB) copied, 1412.7 s, 12.2 MB/s
>
> real	    23m32.736s
> user	    17m52.739s
> sys	    5m0.884s
>

Suddenly you're cpu bound.  So it looks like compression is really 
expensive for some reason.

-- 
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