I agree that it is disappointing that so many vendors seem to have trouble reading the spec. This case is pretty clear. The best the T10 committee could do is add a bit to indicate that the device uses the length from MAXIMUM UNMAP LBA COUNT field for the length of unmaps via the WRITE SAME w/UNMAP=1 rather than the MAXIMUM WRITE SAME LENGTH field. BUT, I'll be very clear that the setting of any such new bit will be bit=0 is backward compatible for COMPLIANT devices, and bit=1 will be the new setting for "backwards" devices - which means they would STILL require a firmware change to tell you they are backwards, and you'd STILL need a blacklist for their older revisions. And this would just makes the hosts job all that much harder! Once a device is broken (violates the spec), there is not very much we can do in the spec to fix it (they have to fix their broken device). Fred -----Original Message----- From: Ewan D. Milne [mailto:emilne@xxxxxxxxxx] Sent: Wednesday, September 27, 2017 12:28 PM To: Martin K. Petersen <martin.petersen@xxxxxxxxxx> Cc: linux-scsi@xxxxxxxxxxxxxxx; Knight, Frederick <Frederick.Knight@xxxxxxxxxx> Subject: Re: [PATCH] sd: Limit WRITE SAME / WRITE SAME(16) w/UNMAP length for certain devices On Mon, 2017-09-25 at 21:46 -0400, Martin K. Petersen wrote: > Ewan, > > > Some devices do not support a WRITE SAME / WRITE SAME(16) with the > > UNMAP bit set up to the length specified in the MAXIMUM WRITE SAME > > LENGTH field in the block limits VPD page (or, the field is zero, > > indicating there is no limit). Limit the length by the MAXIMUM UNMAP > > LBA COUNT value. Otherwise the command might be rejected. > > From SBC4: > > "A MAXIMUM UNMAP LBA COUNT field set to a non-zero value indicates the > maximum number of LBAs that may be unmapped by an UNMAP command" > > Note that it explicitly states "UNMAP command" and not "unmap > operation". > > "A MAXIMUM WRITE SAME LENGTH field set to a non-zero value indicates > the maximum number of contiguous logical blocks that the device server > allows to be unmapped or written in a single WRITE SAME command." > > It says "unmapped or written" and "WRITE SAME command". > > The spec is crystal clear. The device needs to be fixed. We can > blacklist older firmware revs. > Yes, I know that is what SBC-4 says, and I agree that the devices are not conforming. Unfortunately, I've come across 3 different arrays now from 3 different manufacturers that exhibit this behavior. cc: Fred Knight for his opinion on this (NetApp was not one of the arrays that I've run into, though). -Ewan
