Re: USB HD: No Sense / Info fld=0x0 and read corruption

[Ludovico Cavedon <ludovico.cavedon-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Alan Stern wrote:
> On Wed, 24 Dec 2008, Ludovico Cavedon wrote:
>> -it is happening also with 2.6.28-rc8 (which should have the patch, right?)
> 
> What patch?  Do you mean the patch at the end of that email thread?  It 
> affects only Argosy USB drives, not your Western Digital.

I thought also patches
http://marc.info/?l=linux-scsi&m=122443015406309&w=2
were included, but later I realized I was wrong.
I have patched my kernel with them, and now I/O errors get reported!

>> I am not able to understand if this is HD problem or a kernel problem. I
> 
> Partly both.  The HD (or more likely, its USB interface) is responsible 
> for sending those unnecessary empty sense records.  The kernel is 
> responsible for not reporting an I/O error (assuming an error actually 
> did take place).

I think I found out what is happening on the HD side. The SMART self
test fails with a read error. The SMART log reports uncorrectable read
errors. However Reallocated_Event_Count is 0. Searching on the web,
looks like that these sectors have bad ECC, so the cause a read error,
however they are not bad sectors. Is this correct?

My question is: how can this happen? and not just one sector, but at
least a dozen!
Bad HD? (it's new! 93 hrs of activity so far!)

>> am able to replicate it:
>> -2.6.28-rc8 vanilla kernel
>> -2.6.27 ubuntu (intrepid) kernel
> 
> 2.6.27 doesn't go into an endless loop?  This may indicate that 
> eventually the drive stops sending the Check Condition status.

You are right. Most of the read attempts succeed after a a while.
However I found one sector that is causing an endless loop on 2.6.27 and
unpatched 2.6.28-rc8

> It would help to see the dmesg log for when one of these errors occurs.

There are no additional messages. However here it is:
http://pastebin.com/mcfd54a3

> It would also help to know what happens under Windows.  Do the same 
> "empty sense" errors occur?  If they do, how does Windows handle them?

I can try to use usb snoopy to log usb traffic under windows.
Do you know how I can ask Windows "read sector X"?

Thank you for your help,
Merry Christmas!
Ludovico
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