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Raffaele BELARDI <raffaele.belardi@××.com> posted 47418F30.6050607@××.com, |
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excerpted below, on Mon, 19 Nov 2007 14:27:12 +0100: |
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|
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> Most of the resources I've read up to now imply that e.g. /dev/sdc1 is |
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> detected and a 'bad superblock' message displayed when attempting to |
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> mount. |
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> |
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> In my case the kernel is unable to detect /dev/sdc1, after the long list |
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> of read errors below it ends up with only /dev/sdc. |
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> |
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> Does this look like superblock issue, or something worse? |
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|
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If you have a spare drive of the same size or larger, you can try dd, or |
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probably better yet, merge dd-rescue and try it. They copy a file or |
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part of one, in this case an entire block device, from one location to |
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another, "raw". What you want to do is copy the entire bad device, /dev/ |
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sdc above, to the new device. Then you have a copy to play around with |
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without worrying about making the bad device worse before you get |
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whatever you were trying to get off of it, off. |
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|
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dd-rescue is different than dd in that if there are bad blocks, it will |
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run until it starts hitting them, then it will work backwards from the |
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other end until it hits them there, then it'll try blocks in the middle. |
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Thus, if you have good blocks, bad blocks, good blocks, bad blocks, good |
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blocks, dd-rescue recovers more of the disk in a reasonable amount of |
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time, as compared to straight dd, which will try straight thru only. |
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|
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(The problem is that once you start hitting bad blocks, everything slows |
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down, because the system tries and retries the bad block multiple times |
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before giving up, taking minutes to read a block or finally decide it |
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can't, before moving on, where it'd read a good block in seconds. Thus, |
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to work thru even a few hundred bad blocks can take DAYS. Giving up |
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after a few and starting from the other end, then trying in the middle, |
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increases the number of blocks recovered, without sitting there waiting |
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for days for it to work thru all the bad ones and get to the rest of the |
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good ones again, and that's what dd-rescue does for you, automates the |
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give up and try from the other end and then in the middle stuff.) |
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|
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The thing to remember when working with either program is that you want |
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to be **VERY** **SURE** you get the right devices specified, particularly |
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for the output device. If you tell it to write to the device that your |
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main system is on instead of the new empty device, it WILL overwrite your |
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main system device, boot record, partition table, and all. Thus, make |
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TRIPLE SURE you have the right output device specified before you hit |
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that enter key. |
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|
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The reason I'm suggesting dd/dd-rescue is because they'll grab the raw |
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data (what they can of it) directly off of the device you point them at (/ |
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dev/sdc above, but as I said, be absolutely sure the devices aren't |
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reordered after you attach the new one). Since you can't mount the |
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partition, you need something that can grab the info off of the |
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unpartitioned drive itself. Then, once you get a copy to work with, you |
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can check what fdisk says about it and go from there. |
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|
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In fact, if the data is worth it and you have the money, you may want to |
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get TWO replacement drives, one to make a "safe" copy to, and a second to |
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make a working copy (from the safe copy) to. Then you play with the |
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working copy, and if you screw up, you can simply recopy from the safe |
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copy, without having to go back to the damaged drive -- because it's |
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possible you'll only get the one chance to get stuff off of the damaged |
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one. |
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|
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If the damage is severe enough dd-rescue can't pull anything off, |
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consider wrapping the drive in paper for padding and moisture absorption) |
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then plastic (preferably double- or triple-wrapped), then put it in your |
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freezer overnight. There are quite a number of tales of folks that had |
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dead drives that they were able to revive long enough by freezing them, |
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to get the stuff or at least part of the stuff off that they needed to. |
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Keep in mind that as soon as you take it out and plug it in, it'll start |
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warming up, and you may only have a few minutes, if it's bad enough. In |
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that case, if you have just a few smaller files you really want, you can |
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hope the filesystem is usable again, and you may have time enough to |
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retrieve them. If that's not the case, and you need to go for the bulk, |
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then you can write down how far you get, then try freezing it again, and |
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tell dd-rescue to start where it stopped the second time. Of course, you |
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may have a limited number of times even freezing the drive will work, and |
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you likely won't recover the entire thing this way, but if some is better |
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than none... |
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|
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There are special forensics LiveCD distributions out there. Try STD and |
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INSERT (google them, that's how I found them), both based off KNOPPIX, I |
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believe. INSERT is small enough to fit on the small credit/business-card |
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sized CD, 180 MB or some such. STD is a full-sized CD-image, basically a |
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normal KNOPPIX only with enough stuff removed to load the extra forensics/ |
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recovery/etc tools. It even still has some games (Frozen Bubble, etc) on |
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it. They may help you recover something workable off the image you |
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copied over with dd-rescue. Of course, since they have a bunch of |
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programs, including AV and other MS Windows recovery stuff (there's a |
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nice MS eXPrivacy password blanker utility on there, my boss ran into |
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trouble, hadn't created a password reset disk, and I had to use it on his |
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box, yes, it was his), and network troubleshooting stuff as well, you'll |
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probably want to grab them and play around with them a bit to see what |
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they are like, before actually starting to work on recovering your data. |
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|
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Hope that's useful. |
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|
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-- |
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Duncan - List replies preferred. No HTML msgs. |
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"Every nonfree program has a lord, a master -- |
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and if you use the program, he is your master." Richard Stallman |
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|
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-- |
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