ITEM: DB6596L

cfgmgr does not configure more than 8 LUNs on OEM RAID

Response:

ENVIRONMENT:
   OEM RAID device, Fast/Wide SCSI adapter

PROBLEM:
   Customer has an OEM RAID device with 28 logical units (LUNs)
   divided between two systems.  When he runs cfgmgr, only the first
   8 of the 14 LUNs assigned to the system show up.  Customer can
   manually configure the other 6 LUNs as "Other SCSI Disk Drive"
   using the mkdev command.  Since AIX supports 32 LUNs per SCSI
   address, why is cfgmgr only configuring the first 8?

EXPLANATION:
   The SCSI-2 standard specifies that up to 8 LUNs may be supported
   at a given SCSI ID.  Some vendors have developed support for LUNs
   beyond 7 for their devices.  These are typically RAID devices.
   AIX will check the ANSI level in the inquiry data for all disks.
   If the ANSI level is SCSI-1 or SCSI-2, then AIX will only attempt
   to configure LUNs from 0 to 7.  If the disk were to report an
   ANSI level of SCSI-3, then AIX will attempt to configure LUNs
   from 0 to 31.  

   The reason this is necessary is that 32 LUNs per SCSI address is
   not supported by the SCSI-2 standard and the operating system
   would be in violation of that standard if it were to attempt to
   identify LUNs beyond 7.  There has been reported instances where
   SCSI-2 devices will respond at LUN 8 as if it were LUN 0
   (ignoring the high order bits of the LUN), or will hang the SCSI
   bus when going beyond LUN 7.

   The SCSI adapter configuration method will never automatically
   configure LUNs beyond 7 for any device which identifies itself
   as SCSI-2.

WORKAROUND:
   Manually configure LUNs beyond 7 using the long form of the
   mkdev command or SMIT.  To ensure that these LUNs are available
   after reboot of the system, write a script with the mkdev -l
   commands, and create an entry in the /etc/inittab script which
   calls the script.

   For example, if the script is called "raid.add", and is located
   in the /usr/local/bin directory, the /etc/inittab entry should
   look like:

       raid:2:once:/usr/local/bin/raid.add



Support Line: cfgmgr does not configure more than 8 LUNs on OEM RAID ITEM: DB6596L

Dated: August 1997 Category: N/A

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