SD backup while disk is in use
 

I needed to clone a 1.5 TB data drive with roughly 900 GB on it to a 2 TB drive, but needed to use it as the transfer was going quite slowly (started at around 30 MiB/s but dropped to 10).

Obviously, anything that was changed after it was copied would not be up-to-date, but it appears that the operation continued to completion. Thereafter I did a smart update to bring things up-to-date when I went out for a bit and am presently running off of the 2 TB drive without apparent difficulty.

A couple of questions came to mind about this.

This first is, why was a straight erase and copy running so slowly? (I have an external 2 bay SATA enclosure that the drives were in which runs off of a PCI/SATA controller in a FW 800 G4 (dual 1.42 GHz) with OS 10.5.8.

Any thoughts about whether there are drawback to doing things this way?

Thanks

Lots of little files tend to copy slower than big files. It's hard to know what overall speed is going to be... I'd generally expect about 8-20MB/s or so, but less on a G4...