[dm-devel] Losing paths
guy keren
choo at actcom.co.il
Tue Jul 22 22:10:58 UTC 2008
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 at suse.de <mailto:hare at suse.de>>
> Subject: Re: [dm-devel] Losing paths
> To: device-mapper development <dm-devel at redhat.com
> <mailto:dm-devel at redhat.com>>
> Message-ID: <4885F4DF.8010000 at suse.de <mailto:4885F4DF.8010000 at 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 at suse.de <mailto:hare at 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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