Using Rsync to backup to an external drive

https://serverfault.com/questions/25329/using-rsync-to-backup-to-an-external-drive

use rsync with the following flags handily memorable as 'glop' and 'trunc' and 'v'.
rsync -gloptrunc $srcdir $dstdir
A brief guide:

• g - preserve group ownership info
• l - copy symlinks as symlinks
• o - preserve owner info
• p - preserve permissions
• t - preserve timestamps
• r - recurse thru directories
• u - update, skip any newer files
• [n] - no, dont do this, do a dry run instead
• c - checksum, attempt checksums on file blocks when possible (*)
  note: on local filesystems, this get overridden and entire files are copied instead.
• v - verbose

Compatible with FAT32:  rsync -rtv src dst