BIG performance issue with ext3

[paulvarjak at gmail.com]

Can anyone explain this, in the same system?
It's not a hardware issue because I have the same problem in two equal
computers.

Thanks

# time dd if=/dev/zero of=zeros count=1000000
real    0m3.941s
user    0m0.273s
sys     0m3.250s

# time dd if=/dev/zero of=zeros count=1000000
real    0m53.411s
user    0m0.262s
sys     0m3.355s

# time dd if=/dev/zero of=zeros count=1000000
real    0m3.597s
user    0m0.279s
sys     0m3.305s

# time dd if=/dev/zero of=zeros count=1000000
real    0m53.346s
user    0m0.286s
sys     0m3.349s

# time dd if=/dev/zero of=zeros count=1000000
real    0m18.566s
user    0m0.290s
sys     0m3.347s