How to backup and create a copy of a multisite.

Hi,
I have my multisite which is soon to go live and I would like to create a local copy for future testing. I also want to make sure I am doing the right thing with backups.

I have Xamp ready to go locally but I'm not sure how to copy the multisite.

Snapshot only backs up the main site so what should I do if I would like to back up all the subsites as well? If I do use snapshot to backup just the main site does that work fine in a multisite situation.

Thanks,
Nat.