Re: Odd behaviour by ddrescue--seemed to work but did nothing visible (after 8 hours!)

[Robert Backhaus]

You must have had an existing mapfile in the correct directory, perhaps
from a previous recovery, that showed the first 250G as recovered, so
ddrescue continued on from that point.

How to go from here depends on what was in that old mapfile. If it was from
a completed rescue, then all it effectively did was started at ~250GB,
doing a new copy, using the --size parameter and a new mapfile should
complete the copy -

ddrescue -f -s 255G /dev/sda /dev/sdb first250.mapfile

If the mapfile wasn't from a completed run, then you would be missing
chunks from across the disk. I don't know how to go from here. Perhaps
starting afresh would be more reliable. As the disk started off blank, you
could use ddrescue -G on the new disk to create a mapfile from the areas
that are still zeros, but that would require reading the entire disk, which
wouldn't be much faster than re-doing the copy.


On Thu, 26 Dec 2019 21:55 Shahrukh Merchant, <address@hidden>
wrote:

> I cloned a 2T disk to another same-model same-size new disk. The
> destination disk was brand new (not initialized or formatted or
> anything), using, as I have done any number of times before, the following:
>
> ddrescue -f -v /dev/sda /dev/sdb mapfile
>
> Two strange things happened:
>
> 1. ddrescue status after just a couple of minutes when I returned to
> check showed "25% rescued" -- the first 500G had already been copied,
> but that is not possible! The rest of the copy took 7+ hours (which is
> the normal time)--there is no way 25% could have been done in a couple
> of minutes. ddrescue seemingly skipped 25% while claiming to have done
> it. (Incidentally, 32% of the disk is unallocated--no partitions--but
> ddrescue shouldn't know or care about that ...)
>
> 2. When the clone was completed (7+ hours later), the new disk showed NO
> partitions at all. Something was copied during 7 hours for sure, but not
> including the MFT and apparently not including 25% more of the disk
> content.
>
> Here at the contents of mapfile (looks normal to me ...) and the lsblk
> output after the alleged clone operation (NOT what I was expecting). No
> errors were reported.
>
> # Mapfile. Created by GNU ddrescue version 1.24
> # Command line: ddrescue -f -v /dev/sda /dev/sdb mapfile
> # Start time:   2019-12-25 23:29:13
> # Current time: 2019-12-26 06:55:48
> # Finished
> # current_pos  current_status  current_pass
> 0x1D1C1110000     +               1
> #      pos       size  status
> 0x00000000 0x1D1C1116000  +
>
> (Note difference in 0x1D1C1110000 and 0x1D1C1116000 if that's important
> ... 6000 vs 0000 at end.)
>
> # lsblk -oNAME,SIZE,FSTYPE,LABEL,MODEL
>
> NAME     SIZE FSTYPE   LABEL       MODEL
> loop0  788.8M squashfs
> sda      1.8T                      WDC_WD20SPZX-00CRAT0
> |-sda1  39.2M vfat
> |-sda2  11.8G ntfs     RECOVERY
> |-sda3   250G ntfs     OS
> |-sda4  1010G ntfs     Data
> sdb      1.8T                      WDC_WD20SPZX-22UA7T0
>
> (I'm skipping showing sdc which is the USB drive from which I was
> running ddrescue via System Rescue CD.)
>
> /dev/sda and /dev/sdb are exactly the same before and after the image--I
> was expecting sdb to show the same 4 partitions as sda after the
> ddrescue operation as in fact it has done any number of other times. I
> even opened disk manager on another Windows machine to see if it saw
> anything on the newly cloned disk and Windows wanted to initialize the
> disk (no MFT found).
>
> For me, the 25% "instant" jump at the start is the key (I happened to
> notice it just by chance since I checked shortly after starting the run,
> since there was absolutely no other indication of anything wrong) but I
> have no idea as to why that happened or what went wrong.
>
> So ... what's going on???
>
> Thanks!
>
> Shahrukh
>
>