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[Bug-ddrescue] ddrescue slows down by-and-by and will never finish

From: GT
Subject: [Bug-ddrescue] ddrescue slows down by-and-by and will never finish
Date: Wed, 31 Dec 2008 01:45:35 +0100
User-agent: Thunderbird (Windows/20081105)

Hey folks,

I have the following question and we could not find any hint about that problem yet:

We try to rescue a 250 gig hard disk which seems to contain only few errors (another programm found some at about 2% and 50%) and started it with the command

sudo ddrescue -v /dev/sda1 /media/extern/backup/platte22.dd /media/extern/backup/logfile

The hard disc first was left in my PC and the rescue hard disc is an extern USB TrekStor 1TB. We used a UBUNTU boot CD, because the hard disc did not work within my Windows system anymore. Now the disc runs in a Linux system also with the extern USB, but this does not make any difference with the speed.

It started fast with about 30000 MB/s and then slowed down by-and-by to 100kB/s by now at 100 gigs. Important fact: ddrescue holds the speed for some time, then falls down a step, holds the speed again, falls down a step again and so on. So it slows down step-by-step and never speeds up again. This is why the first 100 gigs are rescued in an aceptable time, but with the current speed it would take weeks to finish (and it still slows down on and on, step by step - so it will never finish I think).

It really feels like you take a piece of paper and cut it in two pieces. Then again. And again. The rest becomes smaller and smaller, but you will never finish. There will be always a rest of the paper that you can cut into two pieces.

So what could be the problem and what a possible solution for it?

My opinion is, that it is because of the big file size. But that would be a problem for everybody, so why did no one report this? But if it would be a problem because of errors it would have found more than 1 error until now or at least speeded up again in between, I think? If you use Ctrl-C and restart it, it only ties up to the last rate, also if you let it cool down in between. So overheating can also not be the problem. If you restart from the beginning it will also start as described above at 30000 MB/s and do exactly the same as I wrote and does not find more errors than before. So the disc is not going to die soon and slows down because of that, I think.

So is there any chance to make ddrescue speed up again or work with an constant rate?

This is the actual status:

Initial status (read from logfile)
rescued:   103433 MB,  errsize:    102 kB,  errors:       1
Current status
rescued: 103437 MB, errsize: 102 kB, current rate: 65536 B/s ipos: 103437 MB, errors: 1, average rate: 103 kB/s opos: 103437 MB

Best regards from Germany,

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