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Re: [dm-devel] Losing paths




Does the 'tur' checker take into account unit-attention issues (i.e. when the configuration of a SCSI device changes, the next command coming from an afected initiator (not necessarily to the same LU) should be failed with a 'check condition' error and a 'unit attention' sense code.

if the TUR checker sent a TUR right after the change and before another read/write command was sent - it will be failed, and then the question is, whether the lower-level driver retries the TUR command, or returns an error. any idea?

--guy

Daniel Keisling wrote:
FWIW, I have the same issue under an HP EVA8000. I'm not really certain if directio is a solution as I have only seen the tur checker being used with an EVA. Daniel ---------------------------------------------------------------------------------------------
Date: Tue, 22 Jul 2008 16:55:27 +0200
From: Hannes Reinecke <hare suse de <mailto:hare suse de>>
Subject: Re: [dm-devel] Losing paths
To: device-mapper development <dm-devel redhat com <mailto:dm-devel redhat com>>
Message-ID: <4885F4DF 8010000 suse de <mailto:4885F4DF 8010000 suse de>>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi John, Romanowski, John (OFT) wrote:
 Hi,
We had similar problem last year using sles9 and SVC 4.2.0.2, as you
describe: adding/deleting a LUN causes
 brief path failures for the host's remaining, unaffected LUNs.

We were using tur checker and it turned out that while adding/deleting
a LUN (and some other admin tasks)
the SVC does not respond well to test-unit-ready tur requests; but it
responds perfectly well to normal read
commands. I opened IBM PMR 43118 on that if you want to ask the SVC
folks about it.

Workaround for us was to use readsector0 instead of tur as multipath
path checker.

Recent post here (see July 8, 2008) said multipath-tools is
deprecating readsector0, and to use directio as
path checker, but directio was said to be much slower than tur,
implying tur was better replacement than
 directio for readsector0.

Only for those cases where no actual read-access is necessary.
Not sure what deprecating readsector0 means for us SVC users.
It means you should be using directio there.
Thanks for the information, I'll see to have it included in SLES10. Cheers, Hannes
--
Dr. Hannes Reinecke        zSeries & Storage
hare suse de <mailto:hare suse de>         +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: Markus Rex, HRB 16746 (AG Nürnberg)




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