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Odd behaviour by ddrescue--seemed to work but did nothing visible (after

From: Shahrukh Merchant
Subject: Odd behaviour by ddrescue--seemed to work but did nothing visible (after 8 hours!)
Date: Thu, 26 Dec 2019 08:55:22 -0300
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1

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.)


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???



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