rsync on macOS copies "phantom data" when drive disconnects

I’m trying to copy files off of a drive that is failing. It hasn’t failed yet 🙂

Basically it keeps disconnecting every 30 seconds. macOS then automatically remounts it, but Finder is having issues copying files.

So I’m trying to use rsync -a --progress, but every time the drive disconnects rsync just "keeps going", and fills the rest of the file with… I dunno, something. I’d assume it’d write zeros, but it’s writing actual data according to hexdump. In any case, it’s not accurate data.

I’ve been able to reproduce the behavior by rsync’ing from a random SD card. If I pull the card while copying a 4gb file rsync just zips through and writes a full 4GB file, even though that’s nonsense.

How do I get rsync to stop copying phantom data when a drive is disconnected??

The problem is that in 2020, macOS ships with a version of rsync from 2006.

--timeout=TIMEOUT
       This  option  allows you to set a maximum I/O timeout in seconds. If no data is transferred for the specified time then rsync will exit. The default is 0, which means no timeout.