Re: [PATCH] firewire: sbp2: allow WRITE SAME and REPORT SUPPORTED OPERATION CODES

[Stefan Richter <stefanr@s5r6.in-berlin.de>]

On Dec 02 2012 Stefan Richter wrote:
> On Nov 26 Martin K. Petersen wrote:
> > >>>>> "Stefan" == Stefan Richter <stefanr@s5r6.in-berlin.de> writes:
> > Stefan> I did not try "sg_write_same" on any of the devices; but since
> > Stefan> the two SPC-3 devices are correctly identified as "fully
> > Stefan> provisioned", won't issue WRITE SAME to them either.
>                        ^[the kernel]
> > 
> > What if you have an SSD behind one of them?
> 
> At the moment I only have a single old SSD available which does not
> implement ATA TRIM as far as I recall.
> 
> And the two mentioned OXUF936QSE based SPC-3 devices are four-bay SATA disk
> enclosures whose firmwares only support various RAID modes and require at
> least two bays to be populated.  I.e. I can't test them with the SSD for
> now.  But I suspect that they don't implement thin provisioning anyway,
> particularly translation of WRITE SAME with UNMAP to ATA TRIM.
> 
> But now I found another SPC-3 compliant device in my stash; a dual SATA
> bridge based on OXUF934DSB which supports JBOD with 1...2 disks
> alternatively to striping/ spanning/ mirroring over 2 disks.  I attached
> the old SSD to it, and its thin_provisioning sysfs attribute was shown as
> 0 as well.  "sg_write_same -U ..." on this device in the 10 and 16 byte
> variants ended with Illegal Request/ Invalid command operation code, but
> otherwise without discernible malfunction.
> 
> > Stefan> Hence let's remove the no_report_opcodes and no_write_same
> > Stefan> blacklist flags so that these commands can be used on
> > Stefan> respectively capable targets.  
> > 
> > I just erred on the side of caution. If you are happy without belt and
> > suspenders that's perfectly ok with me :)
> 
> Blacklisting at first was definitely the right approach.  But now that I
> looked at a variety of older and newer devices, I am confident that the
> general Inquiry_Data.Version >= SPC-3 test keeps the wackier among the
> SBP-2 devices safe enough.

(I followed up with https://git.kernel.org/linus/b0ea5f19d3d8.)

> Of course it remains to be seen what happens with ATA TRIM enabled SSDs
> behind the newer SPC-3 compliant bridges, but at this time the risk with
> those seems low.

I now tested
  - ONNTO dataTale RSM4QO (OXUF936QSE) with two Samsung 840 Pro in RAID 0,
  - ONNTO dataTale RSM4QO (OXUF936QSE) with two Samsung 840 Pro in RAID 1,
  - IOI FWBU2-DSATA12 (OXUF934DSB) with one Samsung 840 Pro
and kernel 3.9.

$ grep . /sys/class/scsi_disk/42\:0\:0\:0/*prov*
/sys/class/scsi_disk/42:0:0:0/provisioning_mode:full
/sys/class/scsi_disk/42:0:0:0/thin_provisioning:0
# sg_opcodes /dev/sdg
  Ext Hard   Disk  
  Peripheral device type: disk
Report supported operation codes: operation not supported
# sg_write_same --10 --lba=1 /dev/sdg
Write same(10) command not supported
# sg_write_same --16 --lba=1 /dev/sdg
Write same(16) command not supported
# sg_write_same --32 --lba=1 /dev/sdg
Write same: pass through os error: Invalid argument
Write same(32) command failed

I will send a patch which reverts the drivers/firewire/sbp2.c hunk of
https://git.kernel.org/linus/54b2b50c20a6 "[SCSI] Disable WRITE SAME for
RAID and virtual host adapter drivers".  (As an aside, sbp2.c implements a
transport, not a virtual host adapter.)
-- 
Stefan Richter
-=====-===-= ==-- -====
http://arcgraph.de/sr/

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