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Cc: freebsd-stable@freebsd.org, Ivan Voras <ivoras@fer.hr>
Subject: Re: Some Unix benchmarks for those who are interesed
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Artem Kuchin wrote:
>>> Artem Kuchin wrote:
>>> Hmm. what kind of HDD, RAID or whatever are you using?
>>> My raid pretty much sucks. It is build it on the intel motherboard
>>> LSI Megaraid. But i still get 81Mb/sec when doing
>>> dd if=/dev/ar0 of=/dev/null bs=1M
>>>
>>> How much do you get on this?
>>
>> geom_mirror on 2 desktop SATA drives, but the results of dd are
>> pretty low:
>>
>> # dd if=/dev/mirror/data of=/dev/null bs=1m count=1000
>> 1000+0 records in
>> 1000+0 records out
>> 1048576000 bytes transferred in 17.817686 secs (58850290 bytes/sec)
>>
>> As you can see, results with a single drive are better:
>>
>> # dd if=/dev/ad4 of=/dev/null bs=1m count=1000
>> 1000+0 records in
>> 1000+0 records out
>> 1048576000 bytes transferred in 16.219518 secs (64649023 bytes/sec)
>
> How is it possible that you get 2x file copy perfomance ? What's the
> matter?!

If you use dd on the raw device (meaning no UFS/VFS) there is no
read-ahead. This means that the following DD-command will give lower STR
read than the second:

no read-ahead:
dd if=/dev/mirror/data of=/dev/null bs=1m count=1000
read-ahead and multiple I/O queue depth:
dd if=/mounted/mirror/volume of=/dev/null bs=1m count=1000

You can test read STR best with bonnie (see
/usr/ports/benchmarks/bonnie); or just with DD on a mounted volume. You
should mount with -o noatime to avoid useless writes during reading, or
use soft updates to prevent meta data from taking it's toll on I/O
performance.

- Veronica