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SubjectRe: READ SCSI cmd seems to fail on SATA optical devices...
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On Tue, 2006-11-14 at 11:02 +0900, Tejun Heo wrote:
> Hello, Mattieu Fluhr.
>
> Mathieu Fluhr wrote:
> > The problem is that, on SATA devices controlled by libata, on some big
> > files (like for example a 600 MB file) the READ command seems to fail
> > and outputs garbage (not 1 or 2 bytes diff, but the whole buffer).
> > -> This problem does not come out everytime, and each time on
> > different sectors.
> >
> > Please note that:
> > - it is not chipset dependant (tested on nforce4 and sii3114)
> > - it is not medium or device dependant
>
> Hmmm... Interesting. So, you're reading the media by directly issuing
> commands through the sg interface, right? Can you please try the
> followings?
>
> * Try using /dev/srX or /dev/scdX device instead of /dev/sgX. You can
> use the command SG_IO but the code path is different, so it will help us
> rule out sg bug.
>
> * Perform rounds of read-verify test using standard block interface (ie.
> simply opening /dev/srX and reading it).
I will try this and report the results.

>
> [--snip--]
> > - When I force the bus type to be IDE, our software will then send ATA
> > commands. In this case, everything works like a charm. No errors at all.
>
> What do you mean by 'sending ATA commands'? libata exports all devices
> as SCSI devices. For ATA devices, you can use ATA passthrough but you
> send CDBs to ATAPI devices anyway.
Inside our code, we first guess which the bus type of every device using
an INQUIRY cmd (0x12).
- If the device appears to be a SCSI one, then we send "pure" SCSI CDBs
- For an IDE device, we do, as described in the Annex A of the MMC-5
spec, and pad each CDBs to 12 bytes.

So in the case of a READ CDB, we send 10 bytes if the device is a SCSI
one and 12 for IDE one.


>
> Thanks.
>

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