ddrescue best practices
The source disk is a 300GB PATA boot drive in a mythbuntu BE/FE. I discovered the drive making some "bad noises" one day. When I tried to reboot it, it would not reboot. I left it sit for a few days and yesterday ran ddrescue to a new 2TB SATA drive receiving this report:
Code:
root@mythbuntu:/home/pat# time ddrescue -f -v -n /dev/sda /dev/sdc /home/pat/ddrlog.txt [edit]On further review I found this https://www.technibble.com/guide-usi...-recover-data/ rather thorough and practical guide to some options available to ddrescue users. I'm still not exactly clear about what to do once I isolate the error(s). Some errors I suppose are harmless. Others aren't. How do I tell the difference? Then how do I go about fixing those that need fixing? I also see that R Tools Technology ("R-Studio") has a product called R-Linux (over on the right side of their website menu). Has anyone used R-Linux or the RTT products? Is there any other or better alternative? [/edit] |
As you used "-n", you need to let ddrescue go back and see if it can scrape anything missed.
See the examples in the manual on the homepage here |
Quote:
Code:
root@mythbuntu:/home/pat# time ddrescue -f -v /dev/sda /dev/sdc /home/pat/ddrlog.txt |
You have one 4K sector that is bad. You could write a pattern to that one sector (ie, <Unread>) and then grep search to see which file is associated with that sector. If you were to have some fancy data recovery hardware imaging systems, you would be able to quickly cross reference the unreadable sectors to the file tables.
All-in-all, 4K missing from 300GB is insignificant. |
I'm marking this "solved". I was [lazy and] hoping for a "bigger picture", more comprehensive approach to my particular problem, but there really isn't a one-size-fits-all. ddrescue is a powerful piece of software. It's best practices are completely described in its man page. Once it has done its job, the next piece of software may be called. It may be fsck or something else. Every situation is different. The real solution is to become familiar with all available tools and study the forums. Many thanks to those who weighed in!
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The closest thing I know of to a "big picture" is the Bad Block HOWTO at smartmontools. It covers ext2/ext3 filesystems (ext4 should be similar) and, to a lesser extent, ReiserFS, but not other filesystems. As was mentioned, one bad 4K block in 300GB is very minor, but it's nice to know which (if any) file was affected.
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