BluRay M-Disks are cheaper and more resistant to humidity / heat.
Alas, M-Disks are hugely more expensive than magnetic tapes, even when not taking into account their much greater volume.
The biggest M-Disks are of 100 GB and the cheapest that I see on Amazon (in 25-piece sets) are at about $9 without taxes and shipping. At that price, I can buy not 0.1 TB, but 2 TB of magnetic tapes, which also have a much lower volume, at 18 TB per tape for the older and cheaper LTO-9 cartridges. I can easily carry with me a suitcase with 360 TB of data (20 LTO-9 cartridges), or store it in a safe place. Carrying 3600 M-Disks or storing them in my home would be impossible.
M-Disks may be used only to archive some small amounts of more valuable data, e.g. documents or programs that you have written yourself, a few scanned legal documents, a few more important books, a small amount of music that you prefer, a few family photographs.
For bulk data, if you cannot afford the cost of tape drives, the only alternative is HDDs, but with HDDs you must take care to always use both duplicate HDDs and archive files with redundancy, which allow the regeneration of their content when any not too large part of the file becomes corrupted. You must also take care to migrate the data periodically to new HDDs, after a few years.
Due to their small size I have not tried to use M-Disks until now, so I do not know if my older Blu-ray recorder can write them. There is also the problem that the availability in the future of Blu-ray recorders and readers is uncertain.
I'm a noob when it comes to tape backups. Is copying the same stuff to multiple tapes standard practice?
> There is also the problem that the availability in the future of Blu-ray recorders and readers is uncertain.
LTO drives used to read tapes from 2 generations back, then just 1. LTO 10 isn't backwards compatible. Future availability of compatible tape drives is also uncertain.
Therefore with HDDs I have always written the same data on 2 HDDs, and this saved me a few times, when after several years of storage both HDDs contained a few corrupted sectors, but not in the same places.
With tapes, I also always write at least 2, but frequently even 3, because their low cost makes this affordable. With tapes, the greatest danger is that if a drive malfunctions mechanically while a tape cartridge is inserted, it might damage that tape.
Having at least 2 copies of each tape or HDD also allows their storage in different locations.
Like I have said, I always combine this redundancy of having duplicate storage media with intra-archive-file redundancy, so I typically add 10% redundancy to each compressed and encrypted archive, so that for any corruption that affects less than 10% of the file the content is still recoverable.
I am still using the older LTO-7. While I might upgrade to LTO-8 or even LTO-9, an upgrade to LTO-10 is unlikely, unless great price reductions will happen in the future, which I doubt.
So I am very concerned by the lack of a good archival solution that is affordable by ordinary people and by small businesses, not only by very rich companies.
Microsoft has demonstrated an ideal archival medium (in glass), but for now the cost of their laser system is too great for commercialization. That appears to be mostly a chicken and egg problem, the lasers and the other optical components are too expensive because they currently are produced only in very small quantities, but they cannot be incorporated into a high-volume application, because they are too expensive.
What software do you use for this?
On Gentoo Linux, the name of the software package that provides them is "app-arch/par2cmdline".
"par2create" needs 2 parameters, the amount of redundancy to be added and the name of the input file (which should be a compressed then encrypted archive file).
It produces several additional files, with recovery information. My script creates then a directory, moves there all the files, including the original archive file, and then aggregates the directory with all its files into a single ".pax" archive file. The ".pax" file can then be stored on a couple of HDDs or of tape cartridges.
Before creating the initial archive file, I scan the directories to be archived and I gather all the metadata of the files (names, sizes, timestamps, content hashes), which I store in a database. The metadata can later be used to search for files, to find out from which archival device they should be restored, and also to detect duplicates (by using the content hashes) that may be omitted from later backups.
When retrieving such a file with redundancy, after extracting its component files the "par2verify" utility verifies the integrity and reconstructs corrupted data, if necessary.
For working with tape drives, I prefer to use a FreeBSD server, because the FreeBSD utilities for tape drives and in general for SAS/SCSI peripherals are more convenient and more complete than those of Linux (it is also possible to use a FreeBSD VM on a Linux computer, with PCIe pass-through for the SAS HBA card used to attach the tape drive).
It is inefficient to store small files on tapes, so I usually collect data to be archived on tapes until I reach an amount of about 50 GB, then I compress, encrypt, add redundancy, aggregate again into a single file and then save it into the tape cartridges.
If you are a business of course tape is cheap. Even then, a few usb harddrives are cheap as well and much faster.