On Nov 11 Stefan Richter wrote: > On Nov 09 Elliott, Robert (Server Storage) wrote: > > I recommend broadening this patch. T10 is discussing making READ (10), > > WRITE (10), etc. obsolete in SBC-4 in favor of their 16-byte CDB > > counterparts. > > > > The algorithm should be: > > 1. During discovery, determine if 16-byte CDBs are supported. There are > > several ways to determine this: > > a) REPORT SUPPORTED OPERATION CODES command succeeds and reports that READ > > (16) et al are supported. > > b) READ (16) command specifying a Transfer Length of zero succeeds. > > c) READ CAPACITY (16) command succeeds and reports that the capacity is > 2 > > TiB. > > d) (future) INQUIRY command succeeds fetching the Block Device > > Characteristics VPD page and notices a new field added by the SBC-4 > > simplified SCSI feature set proposal. > > > > Since REPORT SUPPORTED OPERATION CODES is optional, it won't always work. > > READ CAPACITY (16) used to be optional for < 2 TiB drives, so it won't > > always work either. READ (16) will always work, but requires the drive to > > be spun up beforehand (e.g., with START STOP UNIT). > > This won't work. It will crash badly written device firmwares. > > Instead, try the (10) commands on the SBC-4 device and let it respond that > it does not implement these commands. Or have other means to be certain of > SBC-4 compliance without issuing commands that were optional in or not > defined by earlier revisions of the spec. I wonder whether testing for > INQUIRY_data.VERSION >= something is a sufficiently safe test.
Let me revise this: Try READ CAPACITY (10) first (unless SPC-3's INQUIRY_data.PROTECT is set, in which case I don't know what is safer; READ CAPACITY (16) first or READ CAPACITY (10) first). If this showed a capacity > 2 TB, then Jason's suggestion to always only issue READ (16) to all USB attached devices makes a lot of sense to me if it is true that Windows 7 never issues READ (10) to them. That would be what the proposed patch does. What about WRITE and the various other (10)/(16) pairs of commands though? I don't know what's best in case of transports other than USB (after capacity > 2 TB was established). -- Stefan Richter -=====-===-- =-== -==-- http://arcgraph.de/sr/ -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
