For a few hundred TiB, LTO-9 magnetic tapes (18 TB per cartridge) become cheaper than hard disks, despite the huge cost of the tape drive (between $4500 and $5000, but in many places greater prices are shamelessly requested, which should not be accepted; besides a tape drive you need a SAS HBA card and appropriate cables; thus you need to amortize about $5000 through the price difference between HDDs and tapes, to reach the threshold where using tapes becomes cheaper), and they become cheaper and cheaper the greater is your total amount of data, when the cost of the tape drive is amortized over more tapes. One may choose tapes for better reliability even for amounts of data that are insufficient to amortize the initial cost for tape drive + SAS HBA card + SAS cables.

This is especially true when you take into account that regardless whether you use HDDs or tapes, you should better duplicate them and preferably not keep the copies in the same place.

The difference in cost between tapes and HDDs becomes significantly greater when you take into account that data stored on HDDs must be copied on new HDDs after a few years, due to the short lifetime of HDDs. The time after which you may need to move data on new tapes is not determined by the lifetime of tapes (guaranteed to be at least 30 years) but by the obsolescence of the tape drives for a given standard, and it should be after at least 10 to 15 years.

If you keep on a SSD/HDD a database of the content of the tapes, containing the metadata of the stored files and their location on tapes, the access time to archived data is composed of whatever time you need for taking the tape from a cabinet and inserting it into the drive, plus a seeking time of around 1 minute, on average.

Once the archived data is reached, the sequential transfer speed of tapes is greater than that of HDDs.

LTO-9 cartridges have a significantly lower volume and weight than 24-TB HDDs (for storing the same amount of data), which simplifies storage and transport.