quarup :
1. buying an external storage at least as large as the NAS
...maybe I could:
* back up my data from NAS to the external storage infrequently (say, twice a year)
It pays to be sensible about backups. If you have files which will never or rarely change (a library of photos, or music / video selections, for example) then it doesn't make sense to back them up as frequently as active files that you use and modify day to day.
I use a three-tiered system by putting different classes of files in different groups of folders and selecting those groups for backups:
* active files (e-mail, program code I write, teaching material I update and use, etc) get daily incremental and cycled weekly/monthly backups. For me this turns out to be about ~30GB of files.
* static files (music, photos, etc.) get daily incremental and monthly backups. The daily incrementals catch any new items added to the library without the bulk of backing the whole shebang up every week. The monthly backups reset the archive flag on the files so that they're no longer included in the daily incrementals, thus preventing those from getting to large. This works out to be ~100GB of files.
* archived files (install kits, videos, etc.) don't get backed up. I keep two copies on separate 1TB external drives stored offline in different locations.