I have two 1TB single-partition hard disks configured as RAID1, of which I would like to make an off-site backup on a third disk, which I am still to buy. The idea is to store the backup at a relative's house, considerably far away from my place, in the hope that all the information will be safe in the case of a global thermonuclear apocalypse.

Of course, this backup would be well encrypted. What I still have to decide is whether I am going to simply tar the entire partition or, instead, use dd to create an image of the disks. Is there any non-trivial difference between these two approaches that I could be overlooking? This off-site backup would be updated no more than two or three times a year, in the best of the cases, so performance should not be a factor to be pondered at all.

What, and why, would you use if you were me? dd, tar, or a third option?

  • 1
    Maybe you would need to send your backup to the moon because with a "global thermonuclear apocalypse" the earth would be destroyed.
    – Enrique
    Mar 28, 2010 at 18:53

4 Answers 4


Between the 2, tar would be the winner in my book because of the portability that robertpostill mentions. If I were to do something like that on my own though, I would use rsync.

You mention performance not being an issue. I don't know what connection speed you have between the 2 sites, but if you are doing a remote backup and assuming a 512KBps cable modem up-speed you are looking at nearly a month to transfer the full 1TB. Which is why I would take a local copy first (via rsync) then move your disk to the remote host. Subsequent rsyncs will only copy the files that have changed.


For my money I'd do tar, the reason is that a tar archive is more portable than a dd archive. I'd be thinking that you would get some new hardware and then use a rescue O/S to get your disks set up and get the tar archive onto the new hardware. You know that tar will work on a rescue O/S and that even if you use a BSD-based rescue O/S (assuming you're using Linux as your primary O/S) you can still use tar and be confident of the result. dd is much less likely to work on another O/S.

Also you can twin tar with a compression algorithm like gzip or bz2 to get better space utilization.


I would prefer tar over dd for the purposes you're describing. However, I would recommend dar over tar because it can compress each file individually AND it supports incremental updates.


Why not use rsync, rsnapshot, rdiff-backup or something else that does syncing. That way you don't have to wait for the whole 1TB to copy each time.

  • Whoops, that's exactly what Alex suggested, nvm.
    – ptman
    Mar 29, 2010 at 7:15

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