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im looking to use dd to back up my whole hard drive regularly but it takes around 1.5 hours and want to know if there is a faster way to back up.

possibly just by updating the bytes which are different.

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you ought to look at rsync – Sathya Jan 8 '11 at 5:12

The thing is, finding out which bytes have changed will involve reading both devices and comparing each byte. Doesn't sound very fast this way either.

If you're ready to give up 'backing up the entire hard drive' and to instead do the backup at the filesystem level:
1. rsync
2. rdiff-backup

AFAIK, these programs use some attributes like modification time and size which are available at the FS level. So they should speed things up a LOT (especially if most of your files do not change)

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You can backup a single LVM partition (not a whole raw disk as you mention but may still meet your requirements) by taking a snapshot of it, then doing a incremental backup of the filesystem rather than the raw disk. Once you have the snapshot, you could use incremental tar backups or rsync (recommend rsync). You dont strictly need the snapshot - or the LVM, but helps ensure you get a ~point in time filesystem image.

rsnapshot (which is basically a big wrapper on rsync to make it easier to do incremental backups) supports LVM snapshots and incremental backups. I use it to do the above. Note the first sync is still going to take a long time.

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