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My questions boils down to this. If I do "dd if=/dev/sda of=usbdrive" can anybody confirm that this will get everything including mbr/partition information/all four partitions and create a drive that I can swap with the failing internal drive without losing anything? If this is done while the computer is running will it still copy everything? At this point I'm afraid to shutdown the computer for fear of it never starting again.

Secondly, how tolerant is dd of failing drives? Has anybody used it to recover a half dead drive before that can share any potential pitfalls? Did it get the data ok or is this going to be a hope for the best kind of situation?

And lastly, If the usbdrive is larger than the failing internal drive I'll still be able to expand the partitions later so I'm not losing space? this last part seems silly to ask but with my current streak of bad luck I'll end up overwriting some magic bit and forever turning a 640gb hdd into a 500gb hdd.

Also if anybody has a better solution to create a complete clone that gets everything I'm all for hearing about it.

PostScript: I had been making periodic backups however when whatever miasma that killed the laptop struck it also got the NAS :(

Post PostScript: both devices were on a UPS system.

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up vote 1 down vote accepted
  1. yes for mbr/partition information
  2. i can't insure you that dd can recover every bit in every case, but I already used it for such a case. Except I dumped the data in a file on the USB drive, not directly on the disk as I preferred to reinstall everything and extract data from the potentially corrupted filesystem.[1]
  3. yes, I did it with non corrupted disk-dump, with yours I can't be so affirmative. There is a limitation with MBR and disk greater that 2TB, so you can't expend beyond 2TB.

[1] another benefit is that you can mount the dump as read only without altering your dump.

dd bs=Xk if=/dev/sdY of=/mnt/usbdrive/sdY.dd conv=noerror,sync

with X the size (in K) of a block of your disk hardware, usually 4 and Y you crashed disk.

  • noerror avoid stopping the process in case of error
  • sync puts a nullified block if there is a read error
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thanks for your answer. I'm trying it out now. – AvatarOfChronos Jan 14 '11 at 22:14

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