linux-kernel - Re: weird throughput on write to SATA disk

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Date:	Tue, 14 Oct 2008 18:17:56 +0900
From:	Tejun Heo <tj@...nel.org>
To:	kenneth johansson <ken@...jo.org>
CC:	Grant Grundler <grundler@...gle.com>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: weird throughput on write to SATA disk

kenneth johansson wrote:
> On Mon, 2008-10-13 at 18:33 -0700, Grant Grundler wrote:
>> On Mon, Oct 13, 2008 at 3:19 PM, kenneth johansson <ken@...jo.org> wrote:
>> ...
>>>> Can you try "dd oflag=direct if=/dev/null of=/dev/sdb bs=64k"?
>>> I changed to use O_DIRECT and it's much more consistent now. 69-75 with
>>> 74 about 95% of the time.
>> That's low but it could be worse. Many things can contribute to slow
>> disks. 
> Well my main problem was that it was fluctuating so much that can't be
> right. 
> 
>> Favorites are overtemp (See SMART field 194) and vibration (no
>> measurement possible w/o special equipment). "dd" isn't exactly a
>> performance application until one uses really big block sizes (1MB or
>> larger).
> All my numbers comes from using 1MB blocks. but I'm not using dd.
> After removing the logic that actually put some data into the buffers I
> do get about 105 MB/sec using O_DIRECT. I'm doing a full disk write now
> to get a reference plot. Not using O_DIRECT should be almost identical. 
> 
> 
>>> the disk is supposed to have 105 115 sustained
>>> data rate.
>> Where did 105-115 number come from?
> datasheet . they listed two drives in the same column so that was not
> the range it was sustained OD and the model I have max out at 105. 

Can you try deadline scheduler?

-- 
tejun
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