From: Grant Grundler <grundler@parisc-linux.org>
To: Mikulas Patocka <mikulas@artax.karlin.mff.cuni.cz>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
linux-parisc@vger.kernel.org, linux-scsi@vger.kernel.org,
matthew@wil.cx
Subject: Re: sym53c8xx_2 data corruption
Date: Wed, 27 Oct 2010 23:59:22 -0600 [thread overview]
Message-ID: <20101028055922.GE32200@lackof.org> (raw)
In-Reply-To: <alpine.DEB.1.10.1010271803010.18202@artax.karlin.mff.cuni.cz>
On Wed, Oct 27, 2010 at 06:19:32PM +0200, Mikulas Patocka wrote:
...
> Requeuing forever is dangerous anyway, a device returning QUEUE_FULL
> constantly could deadlock the system. Question: is it better to risk a
> deadlock with a broken device or to risk a false timeout under high load?
> --- I don't know --- maybe there are valid cases where the device is
> returning QUEUE_FULL for long time (some raid reconfiguration?) ... do you
> know about them?
This was a problem in multi-initiator SCSI systems and I'm guessing also
an issue for FC SAN. Multiple hosts "compete" for filling the device's
available command slots. If all hosts used available queue_depth
(say 32 commands) and device only supported 64 commands at a time,
then the 65th command from host #3 might get QUEUEFULL status back.
I'm not sure what the difference is to BUSY status. Wikipedia
suggests "QUEUE_FULL" is a hint that the device is already
processing commands from the same initiator.
hth,
grant
prev parent reply other threads:[~2010-10-28 6:06 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20101027012932.3CB6E4FB4@hiauly1.hia.nrc.ca>
[not found] ` <1288155041.19649.354.camel@mulgrave.site>
2010-10-27 9:04 ` sym53c8xx_2 data corruption Mikulas Patocka
2010-10-27 14:46 ` James Bottomley
2010-10-27 16:19 ` Mikulas Patocka
2010-10-27 16:37 ` James Bottomley
2010-10-28 5:59 ` Grant Grundler [this message]
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