Typo, in Box 5. Wrong kernel version Box 5, RHEL 5.4, 2.6.36, dd bs=1024 count=1000000 if=/dev/zero bs=4096k of=/dev/null Anyone had a chance to try this? :-) On Thu, Jan 20, 2011 at 8:16 PM, Mag Gam <magawake@gmail.com> wrote:
Greg,
Yes, I did one very big like 100TB and I still see the regression. I even tried it with your extra dd option. I am wondering if the new kernel (2.6.36) introduced an options I need to set ?
Can someone else try this?
To reiterate the test scenario, Box 1, RHEL 5.1, stock kernel, dd bs=1024 count=1000000 if=/dev/zero bs=4096k of=/dev/null Box 2, RHEL 5.2, stock kernel,dd bs=1024 count=1000000 if=/dev/zero bs=4096k of=/dev/null Box 3, RHEL 5.3, stock kernel, dd bs=1024 count=1000000 if=/dev/zero bs=4096k of=/dev/null Box 4, RHEL 5.4, stock kernel, dd bs=1024 count=1000000 if=/dev/zero bs=4096k of=/dev/null Box 5, RHEL 5.4, 2.6.35, dd bs=1024 count=1000000 if=/dev/zero bs=4096k of=/dev/null
Box 5 takes much much longer.
And all of these boxes are the same model and specs...
On Thu, Jan 20, 2011 at 9:29 AM, Greg Freemyer <greg.freemyer@gmail.com> wrote:
Mulyadi,
You disappoint me. ;(
Just kidding, but discussing dd throughput without the "conv=fdatasync" parameter is just a waste of everyone's time.
And Mag, use a big enough count that it at least takes a few seconds to complete. A tenth of a second or less is just way to short to use as a benchmark.
Greg
On Thu, Jan 20, 2011 at 12:28 AM, Mulyadi Santosa <mulyadi.santosa@gmail.com> wrote:
Hi...
On Thu, Jan 20, 2011 at 10:36, Mag Gam <magawake@gmail.com> wrote:
Running on Redhat 5.1 if I do,
Are you sure you're using that archaic distro? Or are you talking about RHEL 5.1?
dd bs=1024 count=1000000 if=/dev/zero of=/dev/null
I get around 30Gb/sec
Hm, mine is: $ dd bs=1024 count=1000000 if=/dev/zero of=/dev/null 1000000+0 records in 1000000+0 records out 1024000000 bytes (1.0 GB) copied, 1.12169 seconds, 913 MB/s
This is on 2.6.36 SMP kernel compiled with gcc version 4.1.2 20080704 (Red Hat 4.1.2-48).
However, when I do this with 2.6.37 I get close to 5GB/sec
what if you use another blocksize, let's say 4K or even 32K? here's mine (again): $ dd bs=4K count=1000000 if=/dev/zero of=/dev/null 1000000+0 records in 1000000+0 records out 4096000000 bytes (4.1 GB) copied, 1.31167 seconds, 3.1 GB/s
$ dd bs=32K count=1000000 if=/dev/zero of=/dev/null 1000000+0 records in 1000000+0 records out 32768000000 bytes (33 GB) copied, 4.91775 seconds, 6.7 GB/s
see the difference?
IMHO it's a matter of what I call "block merge efficiency"....the more you stuff pages (that fits into a "magic" number), the faster I/O you got.
-- regards,
Mulyadi Santosa Freelance Linux trainer and consultant
blog: the-hydra.blogspot.com training: mulyaditraining.blogspot.com
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