I'm trying to transfer a 4 TB Time Machine backup from one USB 3 hard drive to another. I'm currently using SuperDuper to do it, and it's going to take upwards of two full days to perform the copy, if not longer.
That's significantly slower than the usual maximum speed for copying over USB 3, and I suspect that what's slowing things down is the overhead of copying each file individually, rather than just copying the raw data on the drive, sector by sector.
Given that I just need to duplicate a partition on to another drive:
- Would it result in a usable partition if I did a sector-by-sector copy?
- Would that be faster than using SuperDuper?
- And if yes to both of the above, what are some methods I could use to do that?
I already tried using Disk Utility's restore feature to clone feature, but it got about 5% of the way in and then failed with a weird error about a drive being busy. So I don't think it's reliable enough, and it has no option for resuming where it left off. But that said, it did seem like it was going much faster, and if it didn't fail, it would've taken around 8 hours for it to finish.
edit: for posterity, the reason Disk Utility failed to copy the drive is because my destination drive was dying and loaded with bad sectors. Under normal circumstances it would probably work and be about as fast as
dd. However I like Allan's answer the most because, in case something causes
dd to stop mid-copy, you can restart it from where it left off.