SCSI-ID persistence query...

SCSI-ID persistence query...

[Shobhit Mathur]

Hello,

I have a few basic questions pertaining to SCSI-id
numbering & persistence :

* How do SCSI targets/LUNs get numbered ? My view is
  that the OS numbers them as it receives
cmd-response.
* If the above observation is correct, a disk with a
  particular id during one boot, will not have the
same
  id during the next boot, which can have other 
  consequences...

  My question is: How is SCSI numbering done and how
is
  it persistent across boots ?

- Thank you

- Shobhit Mathur


	
		
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RE: SCSI-ID persistence query...

[Parthiban Manickam - NPD, Chennai]

Hi Shobhit

In case of Directed Attached Storage(DAS)
SCSI ID is configurable using jumper settings.
The vendor will provide the details about 
the configuration. You have to make sure that id
assigned is unique.

In the SAN(FC or iSCSI Based) environment initiator
will assign unique id.

thanks
Parthi

-----Original Message-----
From: Shobhit Mathur [mailto:shobhitmmathur@yahoo.com]
Sent: Thursday, May 13, 2004 4:30 PM
To: linux-scsi@vger.kernel.org
Subject: SCSI-ID persistence query...


Hello,

I have a few basic questions pertaining to SCSI-id
numbering & persistence :

* How do SCSI targets/LUNs get numbered ? My view is
  that the OS numbers them as it receives
cmd-response.
* If the above observation is correct, a disk with a
  particular id during one boot, will not have the
same
  id during the next boot, which can have other 
  consequences...

  My question is: How is SCSI numbering done and how
is
  it persistent across boots ?

- Thank you

- Shobhit Mathur


	
		
__________________________________
Do you Yahoo!?
Yahoo! Movies - Buy advance tickets for 'Shrek 2'
http://movies.yahoo.com/showtimes/movie?mid=1808405861 
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Re: SCSI-ID persistence query...

[Bryan Henderson]

>How do SCSI targets/LUNs get numbered ?

There are lots of different ways that SCSI targets and logical units get 
numbered/named.  (The LUN is one way a logical unit gets numbered).  You 
didn't say which numbers you're talking about, but I'm going to guess from 
some things you say in your posting that you're interested in the Linux 
device numbers (major/minor).

They're pretty much arbitrary and unpersistent.

Linux basically assigns them sequentially to logical units as it discovers 
their existence, which means if everything stays stable across reboots, 
including which devices are visible, which device drivers you load, and 
what LUNs the targets assign to their logical units, you will see the same 
device number for the same logical unit before and after reboot.  In 
practice, this stability is fairly common.  But the more complex your 
system, the less you can rely on that.  In large complex systems, people 
create device special files on the fly, one way or another (e.g. udev), 
such that the device special file name persistently identifies a 
particular logical unit, even though the device number (or even the target 
ID and LUN) are arbitrary.

Re: SCSI-ID persistence query...

[Kurt Garloff]

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On Thu, May 13, 2004 at 04:00:21AM -0700, Shobhit Mathur wrote:
> Hello,
> 
> I have a few basic questions pertaining to SCSI-id
> numbering & persistence :
> 
> * How do SCSI targets/LUNs get numbered ? My view is
>   that the OS numbers them as it receives cmd-response.
> * If the above observation is correct, a disk with a
>   particular id during one boot, will not have the same
>   id during the next boot, which can have other 
>   consequences...
> 
>   My question is: How is SCSI numbering done and how is
>   it persistent across boots ?

It's not persistent by default.
The SCSI devices are just enumerated in the order of detection.

If you look for more persistent device name for 2.4 and 2.6, have a 
look at scsidev.

For 2.6, another option is to have your hotplug scripts call udev 
call scsi_id.

Regards,
-- 
Kurt Garloff                   <kurt@garloff.de>             [Koeln, DE]
Physics:Plasma modeling <garloff@plasimo.phys.tue.nl> [TU Eindhoven, NL]
Linux: SUSE Labs (Head)        <garloff@suse.de>    [SUSE Nuernberg, DE]

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