[CentOS] ext3 filesystem performance question

Hi,

I'm running centos-4.4 on an SMP system with 4 dual core opterons (2.4 GHz),
and 16 GB memory.

The disk drives are 500 GB SATA-Drives.

Wondering about times for dd command performance and rm command performance in an empty machine 
(the filesystem has been made with "mkfs.ext3 /dev/sd...", nothing more)

1. Making a new 3 GB (1024 x 3megabytes blocks) file with dd needs 10.18 sec wallclock time:

taskset 1 time  dd if=/dev/zero bs=3M count=1024 of=~backes/xxxxx
1024+0 records in
1024+0 records out
0.00user 10.02system 0:10.18elapsed 98%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+187minor)pagefaults 0swaps

2. Repeating the same for 3 times:

taskset 1 time  dd if=/dev/zero bs=3M count=1024 of=~backes/xxxxx
1024+0 records in
1024+0 records out
0.00user 11.88system 1:05.26elapsed 18%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+187minor)pagefaults 0swaps

taskset 1 time  dd if=/dev/zero bs=3M count=1024 of=~backes/xxxxx
1024+0 records in
1024+0 records out
0.00user 12.19system 1:04.43elapsed 18%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+187minor)pagefaults 0swaps

taskset 1 time  dd if=/dev/zero bs=3M count=1024 of=~backes/xxxxx
1024+0 records in
1024+0 records out
0.00user 11.85system 1:09.45elapsed 17%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+187minor)pagefaults 0swaps


The wallclock times increase considerably and vary between 1 min 4.4  sec and 1 min 9.5 sec .

Now removing the file needs a wallclock time of 46.7 secs:

taskset 1 time rm -f ~backes/xxxxx
0.00user 2.16system 0:46.77elapsed 4%CPU (0avgtext+0avgdata 0maxresident)k
0inputs+0outputs (0major+166minor)pagefaults 0swaps

Can somebody explain this weird behaviour. All comments are welcome.

Regards


-- 
Joachim Backes <joachim.backes at rhrk.uni-kl.de>
University of Kaiserslautern,Computer Center [RHRK],
Systems and Operations, High Performance Computing,
D-67653 Kaiserslautern, PO Box 3049, Germany
--------------------------------------------------
Phone: +49-631-205-2438, FAX: +49-631-205-3056
http://hlrwm.rhrk.uni-kl.de/home/staff/backes.html
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