From: Stan Hoeppner <stan@hardwarefreak.com>
To: Steven Haigh <netwiz@crc.id.au>
Cc: linux-raid@vger.kernel.org
Subject: Re: Speeding up chunk size change?
Date: Sat, 03 Mar 2012 20:24:25 -0600 [thread overview]
Message-ID: <4F52D259.4050907@hardwarefreak.com> (raw)
In-Reply-To: <4F52BDC7.5070805@crc.id.au>
On 3/3/2012 6:56 PM, Steven Haigh wrote:
> On 4/03/2012 8:42 AM, Stan Hoeppner wrote:
[snip]
>>> blockdev --setra 8192 /dev/sd[abcdefg]
>>
>> Read-ahead is per file descriptor, and occurs at the filesystem level.
>> The read-ahead value used is that of the device immediately underlying
>> the filessytem. So don't bother setting these above.
>
> Interesting - I didn't think that was the case for whole disk arrays -
> but there you go... Learnt something else :)
[snip]
>>> echo 4096> /sys/block/$i/queue/read_ahead_kb
>> Eliminate this line ^^^^
>
> Any insight into why? I would have thought that this would help -
> however I'm not quite sure as to the values - as this is much less than
> one chunk... That also being said, wouldn't it be a good idea to have
> *some* readahead?
You read the answer up above, and commented on it. Maybe you didn't
fully understand? Or maybe it's because you don't know that these two
are functionally equivalent?
blockdev --setra X
echo X > /sys/block/$i/queue/read_ahead_kb
--
Stan
next prev parent reply other threads:[~2012-03-04 2:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-03 19:36 Speeding up chunk size change? Steven Haigh
2012-03-03 21:42 ` Stan Hoeppner
2012-03-04 0:56 ` Steven Haigh
2012-03-04 2:24 ` Stan Hoeppner [this message]
2012-03-04 2:27 ` Steven Haigh
2012-03-04 2:37 ` Bernd Schubert
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