linux-kernel - Re: MD/RAID time out writing superblock

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Message-ID: <20090918170742.GJ2141@arachsys.com>
Date:	Fri, 18 Sep 2009 18:07:42 +0100
From:	Chris Webb <chris@...chsys.com>
To:	Tejun Heo <tj@...nel.org>
Cc:	Neil Brown <neilb@...e.de>, Ric Wheeler <rwheeler@...hat.com>,
	Andrei Tanas <andrei@...as.ca>, linux-kernel@...r.kernel.org,
	IDE/ATA development list <linux-ide@...r.kernel.org>,
	linux-scsi@...r.kernel.org, Jeff Garzik <jgarzik@...hat.com>,
	Mark Lord <mlord@...ox.com>
Subject: Re: MD/RAID time out writing superblock

Tejun Heo <tj@...nel.org> writes:

> Chris Webb wrote:
>
> > Would such very slow (but ultimately successful) flushes be
> > consistent with the theory of power supply issues affecting the
> > drives? It feels like the 30s timeouts on flush could be just a more
> > severe version of the 15s very slow flushes.
> 
> Probably not.  Power problems usually don't resolve themselves with
> longer timeout.  If the drive genuinely takes longer than 30s to
> flush, it would be very interesting tho.  That's something people have
> been worrying about but hasn't materialized yet.  The timeout is
> controlled by SD_TIMEOUT in drivers/scsi/sd.h.  You might want to bump
> it up to, say, 60s and see whether anything changes.

I'll add that to the list of things to check out on the test machine with a
more disposable installation on it! The 15s flushes we're seeing on
superblock barrier writes do already feel dangerously close to the 30s
hardcoded timeout to me: it's only a factor of two.

Cheers,

Chris.
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