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Re: [Bug-ddrescue] ddrescue produces 0 bytes output


From: Scott Dwyer
Subject: Re: [Bug-ddrescue] ddrescue produces 0 bytes output
Date: Sun, 07 Apr 2013 01:21:14 -0400
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:17.0) Gecko/20130307 Thunderbird/17.0.4

I was not going to give my feedback on this issue about the USB bridge, as I have used an external USB bridge with success in the past. But... I just now had an issue where it failed me in the worst way. I have a SATA drive out of a laptop, that a few months ago when read while it was in the laptop had many errors with a pattern that suggested an impact while performing a write. The errors were consistent in the same spots every time. So fast forward to today when I am testing with that same drive, using the USB adapter. Ddrescue did not give any errors, just read slow. But it gave random garbage data where the errors should have been. So it looked like it had a good read without errors, but it gave totally unreliable data! I plugged the drive into my desktop with a SATA cable, and the errors showed up again like they should have. So I have to reluctantly give a -1 to USB adapters. Just giving my experience.


On 3/30/2013 10:36 PM, Jay Ashworth wrote:
----- Original Message -----
From: "Paul L Daniels" <address@hidden>
Jay Ashworth <address@hidden> wrote:

----- Orig
Rogerio is going to hate us. :-)
Let the debating begin... :)
I like that attitude.

Don't *ever* try to do a drive recovery through a USB bridge: pull
the drive out of the housing and hook it directly to a SATA port. You
can't trust a random USB bridge chip to have enough commands to do
everything you need to do during a recovery.
What sort of commands? To date I've not had any problems with
USB2 or USB3 external docking units. I have found no troubles
that I'm acutely aware of with powered USB external-drive
enclosures either (Seagate); sometimes I have had hiccups with
2.5" non-powered bridges, but that's somewhat to be expected
due to the limited power, especially if the drive has a motor
issue. Overall I have found recovery via USB-bridges to be
more dependable than eSATA or SATA directly, particularly if
the drive resets frequently. Though it's likely a
kernel/driver issue I have found that when directly connected
to the SATA interface I often have the drive become completely
no-responsive to the system ( but reestablishes fine if you
reboot ).
I am quoting others; I have never done a recovery attempt through
a USB bridge, based on their recommendations.  Alas, I'd have to go
dig you up references; I often store only the integrated result,
rather than the source material, in my head.

Different anecdotal evidence I suppose.
Probably, but their reasoning rang true for me.

I agree with cool, and you might find it worth freezing it, though
you need to put it in a ziploc and press all the air out beforehand
to avoid condensation.
No matter how much you press out, there's still enough moisture
in the atmosphere contained in the drive that you'll get
condensation on the actual platters when you pull it out of the
freezer. If you must freeze a drive, then I suggest doing so in
a very low humidity environment. I prefer to keep it between
5~10'C so as to avoid dropping below the dew point.
I've only had to do it once, and it helped, but only just enough.

If you ever have to do it, of course, you're trashing the drive immediately
after, but that's true of recoveries in general, so...

Cheers,
-- jra




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