On Sat 03 Sep 2022 at 17:46:39 (+0200), ppr wrote: > Le 01/09/2022 à 00:24, David Wright a écrit : > > > -R --reverse will start an attempt from the end of the disk, and if > > you're extremely lucky, it might copy most of the remaining 960-odd GB > > of data. OTOH it might only confirm that the disk is closer to meeting > > its maker than it was when you started the rescue. > > I am considering using -R option (as suggested by David Wright) to see > if ddrescue can have better transfert rate starting from the other > side of the HDD. My concern is whether or not ddrescue can resume a > job started, stopped, and relaunched with -R option added. ddrescue's > manual says only: > > --reverse > Reverse the direction of all passes (copying, trimming, scraping, > and retrying). Every pass that is normally run forwards will now be > run backwards, and vice versa. '--reverse' does not modify the size of > the blocks copied during each phase, just the order in which they are > tried. > > If I stop ddrescue and add -R option, would the mapfile be able to > handle this (ddrescue started from the beginning and the end the the > drive)?
I don't know the answer to that. For safety, I would copy the mapfile so far made before changing direction, just in case. After changing direction, I would compare the backed up mapfile with the one that's being written to see what's happening to it. Note that the size of the output image may suddenly increase to the total size of the disk being rescued, because ddrescue needs to start writing to the end of it. > I also add some information related to other answers: > > - The destination HDD is an external USB3 one. It is a physical RAID 1 > with two 8To HDD 7200rpm. The commercial name is Lacie 2big raid. The > fact is image is growing and the speed seems to vary (even if never > fast) lets me think it is perhaps the HDD condition which is the cause > of the slow transfer rate. So your diagnostic (image is growing) won't be usable after reversing. But running, say, tail -f on the mapfile might show lines being appended to it. Or repeated diffs between the mapfile and its backup as ddrescue runs. (Your experience with ddrescue is running ahead of mine.) > - I commented out the failing HDD in /etc/fstab and disable > smartmontools tests for this drive. I did not try to mount the HDD. Cheers, David.
