A bunch of robocopy flags to help backup an external drive.

robocopy-backup

robocopy /b /e /xa:s /xjd /sl /a-:hs /mt /v /fp /eta /log:"D:\To\Directory\transfer.log" /tee "C:\From\Directory" "D:\To\Directory"

(Note that the paths don't have a trailing backslash.)

/b -- backup mode (there's a /zb option for restart mode, but it's a whole lot slower)
/e -- copies subdirectories (including empty directories) in addition to files
/xa:s -- exclude system files
/xjd -- exclude junction points
/sl -- copy symbolic links as links
/a-:hs -- remove hidden/system attributes from files
/mt -- multithreaded
/v -- verbose output + skipped
/fp -- full path of files in output
/eta -- time remaining
/log:logfile.txt -- redirect output to file
/tee -- duplicate log to console window

By default, data, attributes, and time stamps are copied. ACL permissions, owner information,
and auditing information are ignored. (You can modify this behavior with the /copy flag.)

Some potentially helpful regexes for the log:

^\s*New File.*?\n
^\s*?\d+[%].*?\n
^\s*New Dir.*?\n

Logfile Analysis'
Unchanged folders always start with a number - if you create a analysis script to exclude all the lines starting with a number you will only see the changes and the summary text in the result. It's easier than using the regexes above that may miss some things.