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Today's Topics:
1. Re: Linux drive access without BIOS detection (Scott Dwyer)
2. Re: How to increase retries within a pass? (Jarkko Lavinen)
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Message: 1
Date: Tue, 25 Jun 2013 21:17:18 -0400
From: Scott Dwyer <
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To:
address@hiddenSubject: Re: [Bug-ddrescue] Linux drive access without BIOS detection
Message-ID: <
address@hidden>
Content-Type: text/plain; charset="iso-8859-1"; Format="flowed"
My first thought: is this repeatable? Meaning, can
windows see it every
time and linux can't? Or did he just get lucky and the drive happened to
load correctly that time? Are you sure the bios didn't detect it? I have
a personal drive that is like that... on most starts it will just click
and not be recognized in bios (or any op system including windows). But
sometimes it would get something just right and be recognized (think the
"firmware" that is stored on a special part of the drive had read
problems). When it was recognized it would work just fine with no
errors, until the next boot and then it would be hell to get back again.
But I don't see any way that windows could see any hard drive that was
not available to the bios... unless it caused the drive to restart again
after booting and luck was involved. So I ask again, is this repeatable?
On 6/25/2013 7:56 PM, Seth Baker wrote:
> I thought recovery was not recoverable through software
means if the
> BIOS doesn't detect the drive, but it turns out not always true. At my
> work, an executive secretary kept important files on a drive that
> stopped booting. I have been a computer technician for 15 years and
> used ddrescue for 5 years. I could not find a way to recover anything
> on the drive. One of the executives wanted to try recovering data
> after I explained all the things I tried This is a man who has no
> formal IT experience, except he told me he has been tinkering with
> computers for the last 40 years. So he plugs the drive into sata port
> and boot up the computer and the drive starts clicking and I see that
> it not detected in the BIOS. After Windows 7 boots up, he goes to
> "Computer" and the drive is there. After I pick up my jaw that has
> just landed on the floor, I start coping over important files. They
> copy at 3 MB/s
which I guess means it is doing it over PIO mode 0, but
> they all copy successfully. How does Windows access this drive without
> BIOS detection? Can I do the same with Linux with RAW option or
> another option in ddrescue? The disk won't show up as a /dev/sdX
> device in Linux. Any ideas?
>
>
>
> _______________________________________________
> Bug-ddrescue mailing list
>
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Message: 2
Date: Wed, 26 Jun 2013 14:56:49 +0300
From: Jarkko Lavinen <
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To:
address@hiddenSubject: Re: [Bug-ddrescue] How to increase retries within a pass?
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On Thu, Jun 13, 2013 at 02:41:33PM +0300, Jarkko Lavinen wrote:
> The documentaion says "Every bad sector is tried only one time per
> pass."
> ... the remaining bad sectors
are very stubborn. Reads stall
> frequently and I have to use timeout and "while true" shell loop to
> continue. Most of the time is spent on the timeouts.
Those reads were stuck since the kernel was in endless retry loop
which was terminated by ddrescue timeout.
There was discuession "ata_eh_link_autopsy: Bug?" in linux-ide about
media errors year ago:
http://comments.gmane.org/gmane.linux.ide/52019The endless retry on media errors has been fixed in v3.5 kernel.
I had been using v3.2 kernel in Debian testing which suffered from
this endless retry problem. In the kernel ring buffer there were
repetitive pattern of read error and its media error aftermath with 8
seconds cycle length. So effectively increasing timeout to 5 minutes
gave 38 retries per sector.
When I tried later
kernel v3.6 with the
fix, there is only one error
in the kernel ring buffer per each sector. Increasing the timeout
does not increase any more the retries per sector. Instead it increased
the number of sectors tried before ddrescue exits.
It takes 8 seconds to read a sector and this gives 64 B/s average read
speed on bad sectors. When I used timeout with v3.2 kernel I saw even
slower average speed due to these numerous retries.
Next I am going to try if I could do bad sector multisampling in user
space.
Jarkko Lavinen
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