Re: CAM Shingled Disk support patches available

> On Jan 18, 2016, at 2:37 PM, Kenneth D. Merry <ken_at_freebsd.org> wrote:
> 
> I have a new set of SMR patches available.  See below for the full
> explanation.
> 
> The primary change here is that I have added SMR support to the ada(4)
> driver.  I spent some time considering whether to try to make the da(4) and
> ada(4) probe infrastructure somewhat common, but in the end concluded it
> would be too involved with not enough code reduction (if any) in the end.
> 
> So, although the ideas are similar, the probe logic is separate.
> 
> Note that NCQ support for SMR commands (Report Zones, Reset Write Pointer,
> etc.) for SATA protocol shingled drives isn't active.  For both the da(4)
> and ada(4) driver this is for lack of a way to plumb the ATA Auxiliary
> register down to the drive.

I’ve plumbed it down, but in a gross, kludgy way to make NCQ Trim work
where the only value in the Auxiliary register needs to be 1. It only takes
up one bit, but it doesn’t change the size of the CCB. If the NCQ Trim
work wasn’t based on the I/O scheduler, I’d have pushed it into head
and would be happy to share code.

AHCI can send it, but it turns out that LSI’s drivers (mpt, mps, etc)
can’t do it due to firmware inadequacies. The ability to send a FIS
in these firmwares looked promising, but it requires a full draining of
other requests, which kind of defeats the purpose of NCQ.

> In the ada(4) case, we need to add the register to struct ccb_ataio and
> add support in one or more of the underlying SATA drivers, e.g. ahci(4).

I believe that changes the size of the CCB, so I tried to avoid
that since I didn’t want to force a recompile of camcontrol(8).
Adding it to the atacmd structure wasn’t so bad, and the CCB size
didn’t completely change. The problem was that the atacmd changed
size and pushed all the other fields.

> In the da(4) case, it will require an update of the T-10 SAT spec to
> provide a way to pass the Auxiliary register down via the SCSI ATA
> PASS-THROUGH command, and then a subsquent update of the SAT layer in
> various vendors' SAS controller firmware.  At that point, there may be
> an official mapping of the SCSI ZBC commands to the ATA ZAC commands, and
> we may be able to just issue the SCSI version of the commands instead of
> composing ATA commands in the da(4) driver.  (We'll still need to keep the
> ATA passthrough version for a while at least to support controllers that
> don't have the updated translation code.)

I looked to implement things here, but didn’t want to invent something that
the T-10 would later reinvent.

> FreeBSD/head as of SVN revision 294105:
> 
> https://people.freebsd.org/~ken/cam_smr.head.20160118.1.txt
> 
> FreeBSD stable/10 as of SVN revision 294100:
> 
> https://people.freebsd.org/~ken/cam_smr.stable10.20160118.1.txt
> 
> Testing and comments are welcome.

So having said all that, I’m totally open to something better.

Warner