Date: Tue, 15 Jan 2013 20:26:42 -0500 From: Karim Fodil-Lemelin <fodillemlinkarim@gmail.com> To: Wojciech Puchar <wojtek@wojtek.tensor.gdynia.pl> Cc: freebsd-hackers@freebsd.org Subject: Re: IBM blade server abysmal disk write performances Message-ID: <50F601D2.3090009@gmail.com> In-Reply-To: <alpine.BSF.2.00.1301152251530.2950@wojtek.tensor.gdynia.pl> References: <CAA3ZYrACHLU-4OyhLdD%2BmfCDR_kubBg-AiVcopL-skqDurE7YA@mail.gmail.com> <50F5BC08.1060700@gmail.com> <alpine.BSF.2.00.1301152251530.2950@wojtek.tensor.gdynia.pl>
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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
>
> ?
>
I'll do the read test as well but if I recall correctly it seemed pretty
decent.
It is quite obvious that something is awfully slow on SAS drives,
whatever it is and regardless of OS comparison. We swapped the SAS
drives for SATA and we're seeing much higher speeds. Basically on par
with what we were expecting (roughly 300 to 400 times faster then what
we see with SAS...).
I find it strange that diskinfo reports those transfer rates:
Transfer rates:
outside: 102400 kbytes in 0.685483 sec = 149384 kbytes/sec
middle: 102400 kbytes in 0.747424 sec = 137004 kbytes/sec
inside: 102400 kbytes in 1.051036 sec = 97428 kbytes/sec
Yet we get only a tiny fraction of those (it takes 20 seconds to
transfer 10MB!) when using dd. I also doubt its dd's behavior since how
can we explain the performance going up with SATA when doing the same test?
Unfortunately, we'll have to move on soon and we're about to write off
SAS and use SATA instead.
Thanks,
Karim.
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