What blocksize should I use?
A reasonable blocksize is around 1 MB to 50 MB, with 10 MB the default. If you are going to make lots of small changes to big files, it might be worth to try a lower blocksize to get improved performance (but you should really test this before you go for it). Generally you should not need to deviate from the default blocksize, unless you know that you have a good reason to do so.