[Bug-ddrescue] A way to check if ddrescue did a good job?

[Théo Koelz]

Hello,

Again not a bug, just a question (and maybe a suggestion). Ddrescue now
claims to have successfully rescued my hard drive, awesome, but a few
strange things happened and that makes me doubtful : I was rescuing a
1TB HDD, the first 400GB went smoothly, it was pretty fast with few
errors, from 400GB to 420GB it went extremely slow (a few hundred B/s at
worst and only a few thousands on average) and then the disk must have
failed : it wasn't here anymore according to Disk Utility and DDrescue
was going over the 500+ GB left to rescue in seconds (over and over ad
infinitum it seemed, but there was no disk activity according to the
motherboard), I then rebooted and the disk was back, I launched DDrescue
again and after not long the disk must have failed again since DDrescue
flagged more than 500GB as bad sectors, I rebooted again and started to
rescue the bad sectors (ddrescue -d -f -r3 ...) and surprisingly things
went smoothly and it was done in like 2 days with only a small bad
sector of 452608B that couldn't be recovered (my source disk is now
flagged as imminent failure though).

Maybe everything is well and I've been lucky, but as I said I'm a bit
doubtful and would like to know if there's a way to check if ddrescue
did a good job or not (my disk was part of a raid 5 so I can't do this
the obvious way, of course I could try to do a raid recovery and see how
it goes but I can't do this before a few days and anyway, in the mean
time, I would prefer to check before hand if the disk was rescued
successfully or not...). I didn't read anything about this in the manual
so I don't know if ddrescue can do that, but it would be useful (one way
to check this quickly could be to select a few random places on both
disks and compare them, but maybe some other software already does
that?).

As usual thanks in advance, you've been very helpful.

TK