[snakes1100]

This error is why you cant back it up:

tar: /full/path/to/folder/htdocs/p: file changed as we read it

I would guess your in a directory or in the same and you have something there that is writting to a file as your try and compress everything, you will need to use an exclude switch in the command to exclude it.

The command you used is fine, there is no need to change to tar.gz as bz2 will do better compression and still use the p in the command to force it to keep the permissions/ownership intact.