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.
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:
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)
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.
I have win 7 scheduled to backup every Sunday, it's only looking at one of my drives at the moment and is backing up to an external HDD. It's a 1TB drive so should take quite a while to fill but the amount of time the backup takes makes me think its taking a fresh copy every time.
It's now 21:34 and I think backup started at about 19:30. It did a full backup earlier in the week of approx 200GB. Is it copying the whole lot again? Or is it just taking its time checking for differences?
Windows 7 Backup is a block based file backup.
This means each block in a file is examined and if a duplicate already exists on the last backup, and this is the important bit, even if from a different file, that block is not saved. Quite good :)
The first backup is always a full backup. The following backups will only save changed blocks. Disadvantage is you cannot manage your backups individually.
The tools built-in Windows 7 really can do the incremental backup. But there is some limitation. For example, you cannot compress your images and perform your backups individually. I used to have the tool built-in System do the incremental backup. But latter, my friend recommended me a free software which not only can do the incremental backup, delete the old images automatically but also can transfer the system to the dissimilar hardware. Now, i backup my hardware with ease.
i suggest you can download it and have a try.