75 lines
3.1 KiB
Markdown
75 lines
3.1 KiB
Markdown
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title = "Introduction to ddrescue"
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date = "2024-12-11"
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updated = "2024-12-11"
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[extra]
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authors = ["Ydreniv"]
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Let’s suppose one of your friends come to you with a computer issue.
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They’ve got a failing hard drive, and want to recover the data stored on their
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device.
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They are quite worried, as they have important files on it, and it’s their
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only copy.
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Of course, this would never happen to you, because you keep multiple encrypted
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backups of all your data, in multiple place.
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Only a worldwide apocalypse would get you a dataloss.
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So this definitely could *only* happen to a friend, or a family member, but
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not you.
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It would be preposterous to think otherwise.
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So anyway, you want to copy the hard-drive.
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You quickly plug it in your computer, mount it and open the file explorer.
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But the mount takes a long time, accessing the files is very slow, and copying
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them does not always work.
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Plus, the [SMART](https://wiki.archlinux.org/title/S.M.A.R.T.) statistics show
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that this drive has *issues*.
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How do you extract the important data then ?
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By the look of it, the vast majority of the drive sectors are fine, so what
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you’re looking for still exists.
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It’s merely hard to access.
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It’s only a hardware problem.
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If you manage to image the drive, you can then either use it as a mounted
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file, or burn it to another drive.
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You could use good old `dd`.
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Maybe this would work.
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But here, with your friend’s disk on its deathbed, you’d like a tool adapted
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for this situation.
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Here comes…
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**[ddrescue](https://www.gnu.org/software/ddrescue/)**.
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`ddrescue` operates on unmounted devices, and will copy a device block by
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block.
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Even better, it has error handling integrated.
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When it cannot read a block, it will either retry or pass it, depending on the
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options you’ve selected.
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And, crucially, it can store its status in a file, meaning that if you stop
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the process, you’ll be able to resume it later.
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This way, you can quickly recover all easily available blocks, while still
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retaining the ability to do several passes on the failing ones.
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I’m still a novice in `ddrescue`, so read the [Archlinux wiki
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page](https://wiki.archlinux.org/title/Disk_cloning#Using_ddrescue) to get
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specific instructions.
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The Archlinux wiki is overall pretty good, and is one of my main source of
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help on Linux, even with other distributions.
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In my experiment, it has been able to recover all the disk’s sectors, except
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for 47 of them.
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I let it run for at least 50 hours I guess (I haven’t counted) over multiple
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sessions.
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I could probably try to make more passes, to eventually recover the full disk,
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but I’m not sure it’s worth it (and even possible).
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It’s reassuring to know that I’ve now safeguarded most of the data.
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Now that I have a mostly complete image, I’ve started trying to read them.
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Unfortunately, the missing blocks do prevent me from simply mounting the
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resulting image.
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So I’ve still gotta do some work to actually get what I wanted (copying the
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files to another drive), but at least I know that the current image is safe,
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and that there shouldn’t be further data loss.
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So if you’re confronted with data recovery, I recommend giving `ddrescue` a
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look. It’s quite a useful tool !
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