El 2020-09-09 a las 16:59 +0200, Bengt Gördén escribió:
On 2020-09-09 11:58, Carlos E. R. wrote:
That is, 14,73 hours. A lot, for a disk with no errors found. ddrescue said initially (yesterday night) that it would take 5:45 hours. This morning it was still running: it said 7 minutes remaining, it took about 14.
A buddy of mine came over with a disc a couple of years ago and we rescued some photo gallery's from a NTFS-partition. During that process I also had problem with slow read of the disc with ddrescue. After we had done the rescuing I kept the disc to experiment on. After some tests I found the -O and -a switch. You can read about it in the manual but my conclusion was that with the switches I could regain the initial read speed. But I suspect that it's a bit of a risk to use that switch due to maybe faulty hw getting even more faulty. Unfortunatley I don't remember the exact command I used at that time. It might have been -a 0.
-a bytes --min-read-rate=bytes Minimum read rate of good non-tried areas, in bytes per second. If the read rate falls below this value during the first two passes of the copying phase, ddrescue will skip ahead a variable amount depending on rate and error histories. The skipped blocks are tried in additional passes (before trimming). If bytes is 0 (auto), the minimum read rate is recalculated every second as (average_rate / 10).
-O --reopen-on-error Close infile and then reopen it after every read error encountered during the copying phase. If '--min-read-rate' is set, also close and reopen infile after every slow read encountered during the first two passes of the copying phase. Use this option if you notice a permanent drop in transfer rate after finding read errors or slow areas. But be warned that most probably the slowing-down is intentionally caused by the kernel in an attempt to increase the probability of reading data from the device.
I don't think it was slow read, but that ddrescue can not do read and write simultaneously, as dd does. i/o graph, more or less: sdc (read): ******** ******* * * * * * * * * ***** ********* ******* sdd (write): ***** ******** ******* * * * * * * * * * * ******** ******** ******* -- Cheers Carlos E. R. (from openSUSE Leap 15.1 x86_64 (Minas Tirith))