reducing I/O and system load

[Denis Solovyov]

>> > I'm using rsync for simple daily back up data from one HD to another. It
>> > takes  about  10  minutes  daily  under  "nice  -n  19".  The problem is
>> > well-known  as  I  see  -  several other services such as httpd or mysql
>> > begin responding slowly  (up  to  10 sec for mysql queries which usually
>> > processed in a small fraction of a second).
>>      --bwlimit=KBPS          limit I/O bandwidth; KBytes per second
MM> --bwlimit only limits the rate of transfer over the network.  Vilius
MM> Puidokas encountered the same problem and traced it to the scanning as
MM> rsync generates the file list.  He wrote a patch that adds a --slow-down
MM> option that makes rsync wait a few microseconds in between scanning each
MM> file.  Find it here:
MM>         http://vilius.multiply.com/video/item/10

usleep(100) in that place of the source shown on the page really helps,
but it dramatically increases the time of rsync'ing.  I guess Vilius'
supposition that usleep(100) for 10k of dirs is 10 sec is a bit wrong,
it seems to be not a simple multiplication.

Best regards,
Denis Solovyov