linux-kernel - Re: deterministic scsi order with async scan

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Message-ID: <alpine.DEB.1.10.0907161022540.9159@asgard>
Date:	Thu, 16 Jul 2009 10:23:45 -0700 (PDT)
From:	david@...g.hm
To:	Matthew Wilcox <matthew@....cx>
cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-scsi@...r.kernel.org
Subject: Re: deterministic scsi order with async scan

On Thu, 16 Jul 2009, Matthew Wilcox wrote:

> On Wed, Jul 15, 2009 at 06:09:22PM -0700, david@...g.hm wrote:
>> is there any way to get deterministic device ordering with scsi async
>> scanning?
>>
>> currently (2.6.30) it seems that the various scsi busses are loaded in
>> the order that they are detected, which can vary from boot to boot
>> depending on how long it takes for the card to initialize.
>
> I think you're confused.  The async scsi scanning was designed to _not_
> move devices around randomly.  There are other asynchronous schemes in
> the kernel, some of which were not designed with the same care.
>
> The SCSI async scan can't do much about it if the busses are detected
> in a different order.
>
>> would it be possible to detect the cards/drives, but not register them
>> until all the detection is complete so that they can be registered in a
>> deterministic order?
>
> That's exactly how the scsi async scanning works.

hmm, in that case how can I troubleshoot why this system is detecting the 
two different PCI-E cards in different orders on different boots.

David Lang

>> having two drives on two different controllers swap positions from boot
>> to boot makes it very painful. yes I can make an initrd that fixes this
>> up in user space by examining each drive and creating links to re-order
>> them, but this is a lot of work to fix randomization that can be
>> prevented in the first place.
>>
>> David Lang
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>
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