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From: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl>
To: Karim Fodil-Lemelin <fodillemlinkarim@gmail.com>
Subject: Re: IBM blade server abysmal disk write performances
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>
> # dd if=/dev/zero of=foo count=1 bs=10240000
> 1+0 records in
> 1+0 records out
> 10240000 bytes transferred in 19.579077 secs (523007 bytes/sec)
>
you write to file not device, so it will be clustered anyway by FreeBSD.

128kB by default, more if you put options MAXPHYS=... in kernel config and 
recompile.

Even with hard drive write cache disabled, it should about one write 
per revolution but seems to do 4 writes per second.

so probably it is not that but much worse failure.

Did you rest read speed?

dd if=/dev/disk of=/dev/null bs=512

dd if=/dev/disk of=/dev/null bs=4k

dd if=/dev/disk of=/dev/null bs=128k

?