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Old 09-10-2013, 10:16 PM   #1
turkvu
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ddrescue running slow after 1TB


Trying to recover a 2TB drive and ddrescue has slowed down dramatically. I've rescued 1106 GB, but it's currently running at 38000 B/s...which looks like it'll take several years to complete.

When I first started I was seeing dramatically faster speeds. I've tried stopping and resuming the process, rebooting, letting the drives cool for hours and then resuming and it remains slow.

It's still in the Copying non-tried blocks phase. I'm wondering if there is an issue with dd and such large disk sizes.

My last try was

Code:
sudo ddrescue -n -dD source destination log
Thoughts?
 
Old 09-10-2013, 10:59 PM   #2
TobiSGD
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Let it run. If this is indeed a recovery attempt repeatedly starting and stopping the process might do more harm than just letting the software do its job. That it runs slow can have different causes, for example that the sectors it currently copies are not readable at the first attempt, but the number of attempts necessary to read the data lies under the threshold that triggers skipping over those blocks.
 
Old 09-10-2013, 11:54 PM   #3
PTrenholme
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Try sudo ddrescue -ndDb 4096 source destination log, and don't worry about "stopping and restarting" ddrescue. With the same log file when you restart, ddrescue will restart from where you stopped it. I suspect your "slowdown" is because the default block size of 512 is quite small for your disk. (I also wonder about the D option. The is usually no need for synchronous writing when writing to a new disk; that option is more useful when you are writing to a bad block and hoping that the drive will use a reserve block when you write to it.)
 
Old 09-13-2013, 10:27 AM   #4
turkvu
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Quote:
Originally Posted by PTrenholme View Post
Try sudo ddrescue -ndDb 4096 source destination log, and don't worry about "stopping and restarting" ddrescue. With the same log file when you restart, ddrescue will restart from where you stopped it. I suspect your "slowdown" is because the default block size of 512 is quite small for your disk. (I also wonder about the D option. The is usually no need for synchronous writing when writing to a new disk; that option is more useful when you are writing to a bad block and hoping that the drive will use a reserve block when you write to it.)
Tried the larger block size and getting rid of the D option. Been running for about a day now, but still at the slow speed (about 40,000 B/s). Really hoping it's just going through a bad patch and it'll speed up soon.
 
Old 09-13-2013, 10:48 AM   #5
TobiSGD
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I had to rescue a 250GB laptop disk yesterday, in the end ddrescue found about 300 bad sectors, the copy action lastet about 8 hours. So with a 2TB disk this can literally consume days. Just let it run.
 
Old 09-15-2013, 10:16 AM   #6
PTrenholme
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A thought: I was just running ddrescue on a questionable DVD and noticed that it got really slow looking at the part of the DVD to which nothing (except the base track) had been written.

Is it possible that only about 1Tb of your 2Tb disk was actually used, and that ddrescue is "spinning its wheels" where there's nothing to be found? (I think that, depending on the file system(s) you've chosen, unallocated blocks may still be in their "pristine" state, even after formatting. Note that this is an assumption on my part - I'm not an expert, or even well informed, on file system internals.)
 
Old 09-15-2013, 05:20 PM   #7
TobiSGD
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For ddrescue it doesn't matter at all in form of data (random or actual data) is present on the disk. HDDs don't have a pristine state, they are always filled complete with data.
 
Old 09-16-2013, 08:41 PM   #8
turkvu
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Quick update - it's been running since my original post, currently at 1122 GB. It was getting errors at one point for 15h, but other than that it's been error free. It seems that once it errors out once it will continue to do so and the only thing that will get it back on track is a reboot.

Still running painfully slow - have seen a few spikes to 150 kB/s, but it seems to have settled in at 40 kB/s for the most part.
 
  


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