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Re: usb connected hard drives and i/o errors.

On Sat, Aug 23, 2008 at 12:07:32PM -0700, Darren Reed wrote:
> I'm not sure if this is purely an i386 issue but I'm dealing with
> it on a pc and I'm not sure it is generic enough for kern...
> The problem is a hard drive that I'm trying to recover data from.
> It's a laptop form factor sata drive, so once removed from the
> laptop, there are not as many options available... the most obvious
> one being to connect it to a USB<->SATA thingy.
> This isn't exactly perfect: it appears that this adapter introduces
> two failure modes:
> - "loud" I/O error (read returns -1)
> - "silent" I/O error (read returns as if it read everything but the
>  data buffer is unchanged.)


> To detect the 2nd, I fill the buffer with a known pattern that is
> unlikely to appear on disk and see if the post-read buffer has
> the same pattern...not exactly ideal.
> I'm looking for recommendations...
> - are there USB SATA/IDE connectors that don't silently report errors?

I hope so;

> - is there something in NetBSD that is ignoring an error?

I don't think so. The high-level drivers are shared for ATAPI, SCSI and USB.
If error were ignored at this level it would be known, I guess.
If it was at the USB level, I'm not sure why it would do it only in some
cases, or for some devices.

> - is there a "raw" mode to access hard drives connected via USB in
>  such a manner that errors are properly seen by the O/S and where
>  the adapter doesn't try to "cover up"?

unfortunably not, the enclosure usually don't give access to the SATA

> What really worries me about the silent errors is that I'm sure many
> other USB disk enclosures also do this and that I've no way of knowing.
> I'm starting to wonder if USB drives are time bombs and if I should have
> been doing something else...although I'd be similarly suspicious of 
> firewire.

Quite possible. They're doing protocol translation, and the error case
is probably not well tested by manufacturers (at last not in all the ways
an (S)ATA drive can fail).

Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference

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