[clug] Recovering data from old disks. Max age observed?

Eyal Lebedinsky eyal at eyal.emu.id.au
Sat Jun 15 09:17:42 UTC 2019

On 15/6/19 6:48 pm, steve jenkin wrote:
> Eyal,
> No idea - ran ‘ddrescue’ with defaults.

The default is 3 passes.

I recently rescued a small HD, initially showing 3 bad sectors and after a few 100 pass runs.
This is what the last mapfile showed:

# Mapfile. Created by GNU ddrescue version 1.22
# Command line: ddrescue /dev/sda /home/partimag/ea-sda.dd /tmp/dd.map -d -r100 -vv
# Start time:   2019-05-21 03:34:38
# Current time: 2019-05-21 03:41:06
# Finished
# current_pos  current_status  current_pass
0x697A0F000     +               100
#      pos        size  status
0x00000000  0x697A0EE00  +
0x697A0EE00  0x00000200  -
0x697A0F000  0xC0A507000  +

The second last line shows one (0x200 bytes) bad (-) sector.

> no paramaters bar source & destination.
> Those are really handy options it has - thanks very much,
> Next drive I try to recover, I’ll look at the options more closely.
> I was impressed with only 17 errors.

Each pass attempts to rescue only the failed sectors, so very quick.
However, you should always use a mapfile (3rd positional arg) to allow doing more passes in followup runs.

I use something like:
	sudo ddrescue /dev/sdX rescue-sdX.dd rescue-sdX.map -d -r100 -vv
-d	use direct disc access for input file
-r100	exit after 100 retry passes
-vv	be very verbose, nice to see if bad sectors shrink

> Filesystem passed fsck and other checks, so not fussed with losses.

Good, bad sectors are often in unused sections of the fs (a mapfile shows where the bad sectors are).


> s
>> On 15 Jun 2019, at 09:57, Eyal Lebedinsky via linux <linux at lists.samba.org <mailto:linux at lists.samba.org>> wrote:
>> How many ddrescue passes did you use? I found that using a large number (say 500)
>> recovered many bad tracks for me when a disk goes funny.
>> Of course, one may rarely get a false positive.
>> cheers
>> [trimmed]
>> --
>> Eyal at Home (eyal at eyal.emu.id.au <mailto:eyal at eyal.emu.id.au>)
> --
> Steve Jenkin, IT Systems and Design
> 0412 786 915 (+61 412 786 915)
> PO Box 38, Kippax ACT 2615, AUSTRALIA
> mailto:sjenkin at canb.auug.org.au http://members.tip.net.au/~sjenkin

Eyal at Home (eyal at eyal.emu.id.au)

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