RE: [PATCH 1/2] Use sdev_scsi2lun for SCSI parallel drivers

Elliott, Robert (Server Storage)
2014-07-04T20:18:42Z

> -----Original Message-----
> From: linux-scsi-owner@vger.kernel.org [mailto:linux-scsi-
> owner@vger.kernel.org] On Behalf Of Douglas Gilbert
> Sent: Friday, 04 July, 2014 2:44 PM
> To: Hannes Reinecke; James Bottomley
> Cc: Christoph Hellwig; linux-scsi@vger.kernel.org
> Subject: Re: [PATCH 1/2] Use sdev_scsi2lun for SCSI parallel drivers
>
> On 14-07-04 07:54 AM, Hannes Reinecke wrote:
> > SCSI-2 defines only up to 256 LUNs with a flat namespace.
>
> My SCSI-2 draft (revision 10b from August 1989) only has
> 3 bit LUNs placed in byte 1 of the command block, in the top
> 3 bits. There are also things called LUNTARs and LUNTRNs
> at the message level.
>
> 8 bit LUNs do ring a distant bell, perhaps after SCSI-2?
>
> Doug Gilbert

The hierarchical LUN structures have some limited size
LUN subfields:
* the peripheral device addressing method includes an 8-bit
TARGET OR LUN subfield, which specifies an 8-bit LUN at the
current level (if the BUS IDENTIFIER field is 0)
* the logical unit addressing method has a 5-bit LUN subfield

---
Rob Elliott HP Server Storage