kern/134488: [mpt] MPT SCSI driver probes max. 8 LUNs per device

[Michel Bouissou]

The following reply was made to PR kern/134488; it has been noted by GNATS.

From: Michel Bouissou <mbouissou at bioimaging.com>
To: Scott Long <scottl at samsco.org>
Cc: bug-followup at FreeBSD.org
Subject: Re: kern/134488: [mpt] MPT SCSI driver probes max. 8 LUNs per
	device
Date: Wed, 13 May 2009 16:24:31 +0200

 On mar, 2009-05-12 at 22:59 -0600, Scott Long wrote:
 > Increasing the max_lun number in the code is not the solution.  Which 
 > arbitrary number should be chosen?  If it's increased to 32, what about 
 > those who want 64?
 
 Well, 8 is as much arbitrary than 32 would be, but 32 would cover a
 wider use spectrum.
 
 SCSI disks enclosures holding 16 to 20 disks are quite commonplace, and
 some show each disk as a LUN on the same SCSI device (i.e. some SCSI to
 SATA enclosures, or some RAID bays with RAID turned off to use ZFS RAID
 instead).
 
 > What about the problems created for those with older
 > hardware that can't handle high lun scanning?
 
 I'm not sure whether this exists. Possibly. My own SCSI card BIOS
 (LSILogic 1030 Ultra4 Adapter) only scans LUNs 0-7 when the system
 boots, *but* that doesn't prevent FreeBSD to use much higher LUN numbers
 when dev/mpt/mpt_cam.c is patched and recompiled for allowing so.
 
 > The correct action requires a significant amount of code to be written
 > and tested; if it were trivial it would have been done already.
 
 Maybe guessing the highest LUN number to scan according to HW type would
 be difficult, but would it be also very difficult to make this a
 parameter that could default to 8 and be set to higher values with an
 entry i.e. in /boot/loader.conf ?
 
 Would be easier than having to recompile the kernel...