Lun 0

Lun 0

[MShetty]

Hi,

Does lun 0 have any special significance ??

Thanks and Regards,
M Shetty

Re: Lun 0

[Martin Peschke3]

Hi,

yes.
E.g., the REPORT LUNS command might be issued to LUN 0 according to SCSI-3
in order to query information about the availability of other LUNs.

Regards,
Martin Peschke



MShetty <mranalini.shetty@patni.com>@vger.kernel.org on 10/18/2002 08:49:42
AM

Sent by:    linux-scsi-owner@vger.kernel.org


To:    linux-raid <linux-raid@vger.kernel.org>, linux-scsi
       <linux-scsi@vger.kernel.org>
cc:
Subject:    Lun 0



Hi,

Does lun 0 have any special significance ??

Thanks and Regards,
M Shetty

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Re: Lun 0

[MShetty]

Hi,

Thanks a lot for all the replies

A piece of code I am reading, sends the Inquiry cmd to lun 0 first and then to
the actual lun to be probed. As only SCSI devices have the concept of luns... I
think the 1st probe to lun 0 is to check if it is a SCSI device but... on 2nd
thought the same can be inferred by probing for lun n.

I have read something which says that some devices may mess up if probed for
luns > 0. Is this true ??


Thanks and Regards,
M Shetty

Re: Lun 0

[Doug Ledford]

On Mon, Oct 21, 2002 at 09:19:12PM +0530, MShetty wrote:
> Hi,
> 
> Thanks a lot for all the replies
> 
> A piece of code I am reading, sends the Inquiry cmd to lun 0 first and then to
> the actual lun to be probed. As only SCSI devices have the concept of luns... I
> think the 1st probe to lun 0 is to check if it is a SCSI device but... on 2nd
> thought the same can be inferred by probing for lun n.

No.  SCSI devices, if present on a given target, must have something on 
LUN 0.  That item on LUN 0 doesn't have to be online, but it has to exist 
and respond to the INQUIRY command.  LUNs > 0 need not exist.

> I have read something which says that some devices may mess up if probed for
> luns > 0. Is this true ??

Yes.  Absolutely.  Lots of CD-ROM drives will hard lock when you try and 
probe for LUNs > 0.

-- 
  Doug Ledford <dledford@redhat.com>     919-754-3700 x44233
         Red Hat, Inc. 
         1801 Varsity Dr.
         Raleigh, NC 27606
  

Re: Lun 0

[Bryan Henderson]

>A piece of code I am reading sends the Inquiry cmd to lun 0 first and then
to
>the actual lun to be probed. As only SCSI devices have the concept of
luns... I
>think the 1st probe to lun 0 is to check if it is a SCSI device

That doesn't make much sense.  It's also true that only SCSI devices have
the concept of the SCSI Inquiry command.  There's no interface with which
you could send an Inquiry command to a device which is not in some way
SCSI.

But I can imagine using such a sequence to distinguish the absence of a
particular logical unit from the absence of the entire physical unit.  It
would be useful in problem diagnosis to know which of those is the case.