In terms of long-term archive strategy, the more formats and copies the better. I love the idea of 128GB Bluray (BDXL, which I have) but the media is ridiculously expensive and prohibitive for most hobbyist or home purposes. At this point we also have little reliability data available for Blueray's long-term longevity, compared to CDs and DVDs at this point in time.
Using a NAS with good backup strategy is good, too. Even a basic operating system load can access the data on a NAS using NFS, FTP, SMB, and other network protocols, and modern OSes will benefit from web-based browsing offered by many NASes. Beware, however, some NASes may not support older protocol versions or only support them read-only (EMC/Lenovo and NFSv3, for instance, or Netgear ReadyNAS and Samba 2.x) I would like to test, but I theorize one could load up a simple AmigaOS 3.1 installation with the demo of Roadshow or AmiTCP and smb-handler, smbclient, or nfs (the latter of which I have no experience on the Amiga.)
External hard drives (which IMNSHO should be considered volatile due to susceptibility to physical shock,) external SSD, and USB thumb drives are inexpensive these days, as mentioned.
But do we trust those for long-term storage? Endurance rates were tested within the past two years and found to be pretty fantastic for certain brands and types, and I have not yet seen a debunking of the process. Longevity is a different matter and Seagate released an article a while back concluding an SSD at rest WILL go "bad" over time, with the exception of certain types of enterprise-class drives.
Multiple formats also ensures that, in theory, at least one of those formats will be readable down the road. Imagine using a good archiving tape back in the day as the only storage format for your archives only to find the drive to read it is dead, and no drives are available. Some formats have worked to overcome this, for instance my DAT72 drive can read formats back to the original 2/4GB DAT though some DAT160 drives cannot, DLT pretty much the same, and even LTO is backward compatible to a certain degree, and while a universally-hated format among my peers Travan did a good job as well but is definitely a dead format. I keep on-hand a number of drives for each of these formats (including some old floppy controller-based QICs) just-in-case as I never know when I will be asked to try to recover one -- a habit which stemmed from an actual case about a decade back.)
Transitioning between an older and deprecating format to a newer one also gives you better long-term guarantees and a good opportunity for refreshing your data and correcting corrupt storage. (This strategy should also be applied to file formats, and thankfully today we have a number of programs which can read formats as old as ARK and LBR and with a little tweaking and emulation you can still read QIC and BKF files.)
Anyway, while not specifically answering the OP, my hope is that my ramblings may help someone avoid long-term loss of important information.
