I needed to do an exact copy of the byte-level contents of one Seagate Barracuda 7200.11 1.5 TB (ST31500341AS) to another identical drive. dd is the obvious tool for the job, but the default settings copy very slowly. This is because the default block copy size is only 512 bytes. After a bit of experimentation, I settled on a block size of 64k as providing the best performance.
dd if=/dev/disk1 of=/dev/disk2 conv=noerror,sync bs=64k
(obviously you will need to specify the correct disk devices for your setup)
Using the larger block size resulted in a speed increase from 7MB/s to an average transfer speed of 37MB/s. It makes a big difference when you’re copying a full 1.5 TB!
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