Re: [linux-usb-devel] Re: /proc/scsi/map

James Bottomley
2002-06-17T16:42:21Z

patmans@us.ibm.com said:
> I agree it would be nice to get the ID via user space, but it is not
> that hard to get the ID, and trying the various SCSI INQUIRY pages
> that supply the ID is not complicated.

OK, how about some hardware scenarios:

I've a scsi array (an LSI 6298) which has no WWN page (0x83) but does have a
serial number in the VPD page. However, the VPD serial number is an
identifier for the array *controller* and thus is the *same* for all the LUNs.
For this beast I have to add in the LUN number to the VPD serial number to
get a unique identifier per device. Worse, the LSI 6298 is multi path. Now I
get a different "unique" identifier depending on path (because different
controllers give different VPD serial numbers), so if I want to identify it
uniquely, I have to use some property of the LUN, like partion UUID.

Or, what about an old 8 bit EMC symmetrix. They have no WWN page and they
embed both a LUN and a *path* identifier in the VPD serial number. To get the
globally unique ID for this one, I have to strip off the path part.

> FYI the various SCSI ID pages and such are described in the SCSI
> primaray command for example the following:

> ftp://ftp.t10.org/t10/drafts/spc3/spc3r07.pdf

Ah, but that's the scsi-3 spec which (finally) cleaned up this unique name
business. However, for SCSI-2 and before, it was an unholy mess, as the two
examples above illustrate. I agree that for all modern devices which are
SCSI-3 SPC compliant, then just asking for the WWN page probably works. The
question is what to do about all the legacy hardware out there?

James