Re: [fedora-virt] porting a disk from lvm to file
On Sun, Aug 22, 2010 at 07:28:50PM +0300, Avi Kivity wrote:
On 08/01/2010 11:41 PM, Richard W.M. Jones wrote:
>On Wed, Jul 28, 2010 at 07:39:30PM +0200, Sven Lankes wrote:
>>You might want to add -c to the ssh cmd to compress the data if the
>>connection between the servers is< 100 MBit/s.
>When writing the original virt-p2v we found the -C option actually
>makes things a lot slower, assuming the common case where you have a
>gigabit network between the servers. It's quicker just to copy
>without the overhead of compression.
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
$ 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
In summary:
Copy rate (no compression): 11.7 MB/s
Copy rate (with compression): 12.2 MB/s
So now compression is (slightly) faster. YMMV.
Rich.
--
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