Date: Wed, 11 Dec 2013 00:57:42 +0100 From: Douglas Gilbert <dgilbert@interlog.com> To: Nathan Whitehorn <nwhitehorn@freebsd.org>, FreeBSD SCSI <freebsd-scsi@freebsd.org> Cc: Hannes Reinecke <hare@suse.de> Subject: Re: [CAM] Widening lun_id_t to 64-bits Message-ID: <52A7AA76.3060208@interlog.com> In-Reply-To: <52A7A69E.3030703@interlog.com> References: <52A7830B.2090803@freebsd.org> <52A7A69E.3030703@interlog.com>
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On 13-12-11 12:41 AM, Douglas Gilbert wrote: > On 13-12-10 10:09 PM, Nathan Whitehorn wrote: >> Modern SCSI hardware often uses 64-bit logical units (LUNs). The patch found at >> http://people.freebsd.org/~nwhitehorn/lun64.diff widens the type of lun_id_t to >> 64 bits, bumps CAM_VERSION, and begins exposing these to drivers that are marked >> as supporting extended LUNs. No behavior is changed except that peripheral with >> very long LUNs that didn't work before will start working. Binary compatibility >> with old code is also kept. There is, however, a chance that some 3rd party >> software might be unhappy about the type widening, so I'd appreciate any testing >> results. Barring any issues, I will commit this on Friday. > > Interesting, Hannes Reinecke is trying to do something > very similar in the Linux SCSI subsystem. His patch set > today will be the third attempt in a year (by my count) > and he might just get over the top this time. There is > some support in my sg3_utils package for the way Linux > is implementing "64 bit LUNs". The sg3_utils package > also supports FreeBSD so I'm interested in what your > mapping will be. > > Now, as you are no doubt aware, SCSI (www.t10.org and specifically > sam5r15.pdf) does not have 64 bit LUNs, it has 8 byte LUNs in > SCSI order (i.e. big endian). Given that major architectures > like i386 and x86_64 are little endian, the mapping between > a 64 bit integer in native form and an 8 byte SCSI LUN is > a bit of a puzzle. That becomes a little harder when you try > for low numbered integers representing the T10 3 bit LUNs > (showing my age), 8 bit LUNs and 16 bit LUNs. > > Down to brass tacks: what exactly will a SCSI REPORT LUNS > WELL KNOWN LOGICAL UNIT number [T10 (in hex): c1 01 00 00 > 00 00 00 00] be in one of your 64 bits LUNs? Will that be > the same in little endian and big endian architectures? > There is also the representation of that LUN in logs; for > example lun=13907397124296802304 is not very intuitive. > > More examples would be great, perhaps from the 4, 6 and 8 byte > "extended logical unit addressing format". > > > Robert Elliott who has been a T10 technical editor has written > a paper on this subject but google fails me, perhaps someone > else can supply the url. His advice was too late for Linux > and perhaps it is already too late for FreeBSD. The document I was trying to find was a www.t10.org proposal: 06-003r1, see its overview for a rationale. The Logical Unit Representation Format section was accepted and can be found in sam5r15.pdf section 4.7.2 Doug Gilbert
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