Clarify ddrescue options

Here are some questions about ddrescue's options/parameters.

1. Please clarify what the "-t" or "--truncate" option is for. When should it be used? How does it affect the image file? Have you used it?

2. "-i" and "-s"
I know these are related, but I'm not sure how. Here's what I think. Let's say I have a 100GB drive. The following command...

sudo ddrescue -i4000M -s500M /dev/sda /media/recover/test.img /media/recover/test.log

makes ddrescue start its work 4GB from the beginning of the drive and to recover 500MB of data. Is this right? How large will 'test.img' be in this case? When should "-i" and "-s" be used?

ddrescue has had trouble with the last few drives I've worked on. I suspect the drives had problems internally. But here's what happened. ddrescue would start out at a great rate recovering data (~18MB/sec). But at the first bad spot, it would slow to a crawl (<1kb/sec) and stay there until I #1 pressed Ctrl-C, then #2 removed power from the drive. Only then would I get the "interrupted by user" message. I noticed that when ddrescue reached these spots, I would hear unusual sounds coming from the drive, as if it were stuck. I kept expecting ddrescue to just move on and make a big jump, say several gigabytes ahead, but it never did.

I'm at a loss here. What do you recommend for cases like this? The last drive I worked on, ended up dying completely due to the excessive plugging, unplugging, and re-plugging to get ddrescue to resume.

I welcome your input. Thank you!

Hi. I don't really know what

Hi.

I don't really know what the truncate option is for.

The -i and -s options work as you mentioned. -i4000M -s 500M should create a 500 meg image. It should be used when you want to recover a selected portion of a drive. For example, if there is data at the end of a drive and nothing in the middle, you can skip to the end sooner.

Why would you expect ddrescue to jump ahead several Gigs? If you want it to do that, make it do it yourself using the same image file and log file and by using the -i option. It sounds like the drives do have hardware problems, but getting data back at >1kb per sec is better than a few b per second or nothing at all.

What do I recommend? Don't unplug a damaged drive. Ever. If it's spitting out data, it's good. The enemy of "good" is "better". Every time you restart a damaged drive, you run the risk of it not powering up again. I've had drives powered on for weeks for that reason.

I copy the image onto another medium while it's being made to work on retrieving data from it.

What if the "rescued" field

What if the "rescued" field never changes once the drive reaches a bad spot? That's what's been happening. ddrescue will zip along recovering data until a bad spot is encountered. Then everything grinds to a halt. I've left the drives untouched for hours and hours when this happens and the "rescued" field never increases. Only when I forcefully unplug the drive and resume at a farther along position does it continue forward. And this is counterintuitive to me. I thought that's what ddrescue was supposed to do. Once it encounters a bad spot, mark it bad, then jump ahead to a good portion of the drive. Come back and split the error areas at the end. It these cases, ddrescue is never getting a chance to skip and move forward. The drive just sits there spinning and making a fluttering sound occasionally and never moves on.

I don't think it's wise to just let ddrescue continue to make the drive sit at a bad spot indefinitely until a miracle happens and it moves on. There has to be an alternative. It's almost as if the drive stops responding. Even Ctrl-C will not register until I manually unplug the drive. Like you said, this is all probably due to failure within the drive. But it seems to at least respond initially. I wish I could record what I'm trying to describe. That might make it easier to troubleshoot.

What do you think?

I think you should try using

I think you should try using a different computer. It sounds like your computer is freezing when trying to read the bad spots and that's not normal.