linux-kernel - Re: Problems with the block-layer timeouts

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Message-ID: <490F0822.6010406@emulex.com>
Date:	Mon, 3 Nov 2008 09:18:10 -0500
From:	James Smart <James.Smart@...lex.Com>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	Alan Stern <stern@...land.harvard.edu>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	SCSI development list <linux-scsi@...r.kernel.org>,
	Kernel development list <linux-kernel@...r.kernel.org>
Subject: Re: Problems with the block-layer timeouts

Jens Axboe wrote:
>> While I'm on the subject, there are a few related items that could be
>> improved.  In my tests, I was generating I/O requests simply by doing
>>
>>       dd if=/dev/sda ...
>>
>> I don't know where the timeouts for these requests are determined, but
>> they were set to 60 seconds.  That seems much too long.
> 
> Fully agreed, as Mike mentioned this actually looks like a dumb udev
> rule that didn't have any effect until this generic timeout work. For
> normal IO, something in the 10 second range is a lot more appropriate.

Yes and no. For direct-attach storage with no other initiators, ok. But 
for larger arrays, potentially with multiple initiators - no.  I can 
name several arrays that depend on a 30 second timeout, and a few that, 
underload, require 60 seconds.  I assume that there's usually "best 
practices" guides for the integrators to ensure the defaults are set right.

-- james s
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