Re: [Networker] The volid on tape and the one in media base is not the same!

2008-05-27 14:41:52
Subject: Re: [Networker] The volid on tape and the one in media base is not the same!
From: A Darren Dunham <ddunham AT TAOS DOT COM>
Date: Tue, 27 May 2008 18:33:32 +0000
On Tue, May 27, 2008 at 08:16:45PM +0200, Oscar Olsson wrote:
> On 2008-05-27 18:32, Davina Treiber revealed:
> DT> Solaris needs persistent binding from the WWNN to the SCSI address, so
> DT> this depends on the HBA used.
> To my knowledge, this statement is incorrect. We don't use persistent 
> binding or any other tweaks to run our networker installation, which is 
> running on Solaris 10.
> First, when a reconfigure is done, the tape devices found are mapped into 
> the /dev/rmt device tree. These device files will remain there until 
> removed.

This is the mapping from the logical tape name to the Solaris device
name.  In most circumastances, it is stable.

> If you add more tapes or replace a tape drive with one that has a 
> different WWNN, it will create a new device file/number for that drive and 
> leave the old one untouched.

The mapping from the loop/fabric device to the "Solaris device" depends
on your FC drivers.  The Sun SAN (Leadville) stack is nice because it
doesn't do a mapping.  It just shows the WWN as part of the device.  So
the Solaris device name is stable.  Fortunately, this is becoming much
more widespread.

Other driver/HBA combinations do not necessarily do this.  They may map
the first WWN seen (or the lowest numbered port on the switch) to
"target 0" or "target 1".  Unless that mapping is made explicit, it can
change (especially during a reboot when a topology change has occured
like losing a drive).

> Furthermore, we have found that if drives are using the same WWNN, SOlaris 
> will always map them in the same order for each reconfigure (after erasing 
> everything in /dev/rmt). Although, our drives never change WWNN since our 
> Spectra T950 gives them this address based on their location in the 
> library chassi, even though they are direct fabric attached LTO-4
> drives.

That may be true for your installation, but "Solaris" does not guarantee
it.  It depends on the fabric drivers in use.


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