bwlimit on rsync locally

[Reeve Yang]

Does "bwlimit" option really work on rsync locally? We have one type
of harddisk and want to slow down rsync I/O on disk because I don't
want the disk head gets too hot. While I'm trying to use --bwlimit
option, it looks the rsync speed was slowed down, but iostat is not
improved at all. In both case the block written speed is increased by
the same amount.

How could I really slow down I/O while using rsync? Any help would be
greatly appreciated.

Regards,
- Reeve

rsync without --bwlimit:
> iostat; rsync -a -r --stats swapfile swapfile.rsync; iostat

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               7.53       103.43       421.27   64549578  262909196

Number of files: 1
Number of files transferred: 1
Total file size: 2147483648 bytes
Total transferred file size: 2147483648 bytes
Literal data: 2147483648 bytes
Matched data: 0 bytes
File list size: 73
File list generation time: 0.063 seconds
File list transfer time: 0.000 seconds
Total bytes sent: 2147745923
Total bytes received: 42
sent 2147745923 bytes  received 42 bytes  23472633.50 bytes/sec
total size is 2147483648  speedup is 1.00
Linux 2.6.22.1-33.fc7 (rxyang-lx)       03/27/2008

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               7.57       108.87       427.92   67955562  267094188

rysnc with --bwlimit:
 >  iostat && rsync -a -r --stats --bwlimit=2500 swapfile
swapfile.rsync && iostat
Linux 2.6.22.1-33.fc7 (rxyang-lx)       03/27/2008

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           1.94    3.39    4.11    0.34    0.00   90.22

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               7.57       107.96       426.21   68539642  270572036


Number of files: 1
Number of files transferred: 1
Total file size: 2147483648 bytes
Total transferred file size: 2147483648 bytes
Literal data: 2147483648 bytes
Matched data: 0 bytes
File list size: 73
File list generation time: 0.061 seconds
File list transfer time: 0.000 seconds
Total bytes sent: 2147745923
Total bytes received: 42

sent 2147745923 bytes  received 42 bytes  2543216.06 bytes/sec
total size is 2147483648  speedup is 1.00
Linux 2.6.22.1-33.fc7 (rxyang-lx)       03/27/2008

avg-cpu:  %user   %nice %system %iowait  %steal   %idle
           1.94    3.39    4.11    0.34    0.00   90.21

Device:            tps   Blk_read/s   Blk_wrtn/s   Blk_read   Blk_wrtn
sda               7.61       112.63       432.78   71598154  275107508