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Date: Tue, 15 Jan 2013 17:45:54 -0500
From: Karim Fodil-Lemelin <fodillemlinkarim@gmail.com>
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To: freebsd-hackers@freebsd.org
Subject: Re: IBM blade server abysmal disk write performances
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On 15/01/2013 4:54 PM, Wojciech Puchar wrote:
>>
>> # 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
>
As you mentioned the dd file tests were done UFS and not on raw device. 
I will get those numbers for you.

Thanks,

Karim.