Trouble backing-up with "dd"
Hi guys,
I've been running a few comparitive backup tests on my Acer Aspire One netbook between Acronis, Clonezilla and the good ol' "dd" command. Clonezilla came out tops (after I disabled a couple of really DUMB default options that were causing it to fail.) Then Acronis (effective back-up in less than 5 minutes; restore in 32m). Lastly and leastly, "dd" which was *awful*. Bear in mind this computer's main partition is a tiny 7Gb. dd took 107 minutes to back this up, and a whole THREE HOURS to restore it! Unbelievably slow as I'm sure you'll agree. Plus when the restore finished and I re-booted, the computer reported it had zero free disk space. And I mean ZERO. The command I used (from an external usb Knoppix live CD) was "sudo dd if=/dev/sda5 of=/dev/hdc1" and the backup partition size was 8Gb. I've never had a bum result with "dd" before, so where did it all go wrong? TIA, CC. |
Keep in mind that dd is REALLY DUMB---it happily copies all the bytes including the empty space.
Also, the speed of dd will depend on the choice of block size. The optimum depends--in turn--on the size of your RAM. |
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Did you say you copied an 8Gb partition to a 7Gb one? That'll be why.
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These are good instructions for backing up partitions with dd. You're better off writing the image to a file rather than directly cloning one partition onto another. I think my 20Gb partition takes about 20-30min to back up and 10 min to restore with those instructions (block size 1k - maybe I can increase this but I'm not sure)
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Well thinking about it, I might be wrong. The filesystem on your system partition is only 7Gb, and cloning it onto a larger partition shouldn't change that - if you mount the backup partition, you should see only 7Gb total space, I think. But still I think this must have something to do with it. Definitely recommend using a gzipped image file if you just want the copy for backup! bzip gives somewhat better compression but is way too slow for this IMO.
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using dd:
if you restore a 10 gb backup to a 5 gb hard drive, the backup will truncate. so any data beyond the 5 gb barrier will be non-existant on the restored hard drive. if you restore a 5 gb backup to a 10 gb hard drive then the restored harddrive will look like a 5 gb harddrive (essentially half the harddrive will be unusable space). |
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