Message-ID: <404E2788.1060108@tmr.com>
Date: Tue, 09 Mar 2004 15:22:32 -0500
From: Bill Davidsen <davidsen@tmr.com>
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To: Mike Fedyk <mfedyk@matchmail.com>
CC: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: questions about io scheduler
References: <1wjF1-2yG-19@gated-at.bofh.it> <1wk7X-31w-1@gated-at.bofh.it> <1wwCd-Pi-5@gated-at.bofh.it> <1wx5r-1qI-9@gated-at.bofh.it> <1wxyd-1WX-1@gated-at.bofh.it>
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Mike Fedyk wrote:
> Timothy Miller wrote:
> 
>>
>>
>> Mike Fedyk wrote:
>>
>>> Nick Piggin wrote:
>>>
>>>>
>>>>
>>>> Kyle Wong wrote:
>>>>
>>>>> 2. Does io scheduler works with md RAID? Correct me if I'm wrong,
>>>>> io-schedular <-->  md driver <--> harddisks.
>>>>>
>>>>>
>>>>
>>>> It goes md driver -> io schedulers -> hard disks.
>>>
>>>
>>>
>>>
>>> There is an IO scheduler per disk.
>>>
>>> So MD submits the data to each disk through the IO scheduler.
>>>
>>> This allows you to have the heads on each disk in the array at 
>>> different locations, and helps keep response times lower for seeky 
>>> loads.
>>
>>
>>
>> Say you've got a RAID1.  In this case, MD could send the read request 
>> to either device.  How does it decide which one to use?
> 
> 
> The one with the drive head closest to the data.

Or hopefully the one not in use if one is busy...

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