Thanks, yes they do and I think I've figured it out. THey show that the only thing changing is that the amount of data stored has gone up. It turns out my sister has been backing up full images of her laptop to the NAS. It went from storing a few hundred gigs to 2.5TB. I've deleted a bunch of old backups and gotten the storage down to about 300 GB. Synology's Glacier Backup app help says that they will delete old files after 3 months to avoid the charges Amazon levies on deleting files newer than 3 months. I guess we'll see what happens in January!