SCAM and boot devices

dallas at dallas at
Tue Feb 13 14:23:18 PST 1996

* From the SCSI Reflector, posted by:
* dallas at

There are a number of issues here and a lot of potential 
to dive into a rathole of discussion, but here are my views 
on this topic.

First and foremost media labels are not the answer nor is it
the responsibility of the hardware adaptors, this is strictly
a host OS issue. 

Second, SCSI-2 does not have the mandatory mechanisms that allow 
the OS to identify a device uniquely.  While there is a Vital Product
Data page of Unit Serial Number, this page is optional and can be
quite long to use to Id a device.  While this serial number along
with Vendor ID and Product Id can ID the device uniquely the storage
requirements may soon strip out any benifit based on the number of 
devices (this remains to be seen).

Third, SCSI-3 does have the mechanism to ID a device (WID+Logical unit
identifier).  It is with SCSI-3 devices that the OS can now at boot 
and at run time change physical pathing to any SCSI-3 device on the 
fly (LIPs on Fibre Channels).  What the OS must do is get rid of 
of the concept of a physical device and define devices as logical 
objects.  Once this transisition is made then the rest falls into place, 
just like there is a S2P layer, the OS must have a L2P (Logical to Physical)


------- Replied-To Message

Date: Tue, 13 Feb 96 16:08:48 EST
From: at (Eddie.Williams)
  To: scsi at (SCSI Reflector)
Subj: Re: SCAM and boot devices

* From the SCSI Reflector, posted by:
* ewilliam at folsom.ColumbiaSC.NCR.COM (Eddie.Williams)
On Feb 12, 11:25am, "Lohmeyer, John" wrote:
> Subject: Re: SCAM and boot devices
> * From the SCSI Reflector, posted by:
> * "Lohmeyer, John" <JLOHMEYE at>
> *
> [soapbox on]
> The "right" solution is for the BIOS and OS vendors to solve the problem. 
>  The BIOS guys need to examine the volume labels on all of the mounted media 
> and pick the boot device (or allow the user to pick the boot device as with 
> OS/2's boot manager).  This is more work than just always booting from ID 0 
> or ID 6, but it is necessary to support the Plug-and-Play philosophy.
> The OS vendors need to adopt a more flexible solution to media management 
> than merely assigning drive letters in the physical media order.  Jumbling 
> drive letters is almost as bad as not booting.
> Apple Computer has solved this problem years ago by not using drive letters 
> and instead naming the disk volumes.  It is time for the other OS vendors to 
> borrow this enlightened idea.  I've expressed this thought to several 
> Microsoft people and have always been pushed back with statements like, 
>  'Drive letters are really engrained -- maybe in the product after the one 
> we've working on now'.  Unfortunately, this is one of the reasons PCs remain 
> more difficult to use than Macs.
> [soapbox off]

This only helps for disks.  What about tapes, CDs, printers, etc?  Writing
to the wrong tape could cause some serious problems too.

Eddie Williams
Ed.Williams at ColumbiaSC.NCR.COM
(803) 939-2073

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