I'm working on a bash script that duplicates files from one "source" pendrvie to multiple others (also formatting drives to FAT32 if they don't mount).
I'm copying the files with rsync.
I've noticed that rsync finishes pretty quickly, sometimes reporting ridiculous write speeds like 500 MB/s, but usually staying at 15 MB/s.
The catch is that afterwards - unmounting the drives can take as long as minutes, and I figured out that it's because of the system disk cache, and asynchronous I/O.
I wonder if mounting the drives in "sync" instead of the default "async" mode would allow the rsync processes to show real writing speeds, and spare the lengthly unmouning, that can't be easily monitored.
I guess it'd be easier to track the real progress and produce a sensible ETA, but I'm afraid I'll hurt the performance somehow, and disable some cool features (for example forcing each copy to be re-read from the source drive instead of the RAM cache).
What benefits and drawbacks can sync produce over async is this particular usecase?