You can archieve unfrequently used files from your storage ( the storage area that saving your backups,pictures…etc). However, the problem about archiving to another media is the problem about indexing, namely, forgetting what you have moved to another medium.
So simple solution is to create basic indexes with tool “ncdu” and exporting this file for future use.Here are the steps and sample usage.
ncdu -o /export.file /mnt/2000
export.file => The basic index file of the filesystem or directory.
Then you can move or change the directory but keep this index file as reference that what has been moved. You can read the index file with the same tool again.
ncdu -f /export.file
Sample Output is :