How do I do this???

[wuzzbert]

I have an external hard drive (A) that I write files to all the time.

Every so often I copy it to a second external hard drive (B) so I have two copies in case anything goes wrong.

How do I only copy the changes Ive made to (A) usually being additional files I've created without having to pick them out before copying to (B).

The only option I seem to get is "Replace" or "stop" on my Mac. If I replace, it takes ages as it completely re-writes (A) on to (B) and its over a 1gb.

Im using OS X El Capitan and the Time Machine facility is no good as my Macbook Air's storage capacity is not large enough for this amount of data unless I'm missing a trick!!!

Can anyone help please?

 

[ocabj]

https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/rsync.1.html

Common local rsync example:

rsync -apv <source_path> <target_path>

 

[wuzzbert]

https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man1/rsync.1.html

Common local rsync example:

rsync -apv <source_path> <target_path>

That's a bit complicated for me, is there no app in the App Store I could download that does it all for me??

 

[chown33]

That's a bit complicated for me, is there no app in the App Store I could download that does it all for me??

Carbon Copy Cloner uses rsync to make its clones, and it probably isn't alone in that.
https://bombich.com

Did you search the App Store for the keyword rsync or sync?

 

[CoastalOR]

That's a bit complicated for me, is there no app in the App Store I could download that does it all for me??

+1 for Carbon Copy Cloner, my favorite.
or
Another option that I have had good luck with is ChronoSync.

I use both and both will do what you want.