_I_ know. The tape wins hands down. There are many industries where documents and data must be kept for 10/20/25 years, sometimes even longer. The latter are usually microfilmed (or todays equivalent), the former are stored on tape. Tape is far more reliable than disk if both are sitting on a shelf. As you say it was designed for it. Disk was not. Most larger corporations that are moving to disk based backup don't put disks on a shelf (like HOSO users often do). They maintain them with power on in a raid setup. Then they routinely scan them for failed drives and replace the drives as they fail.
Absolutely true - this is exactly what we do: disk to disk to tape. And the disk backup is a rolling archive, it contains snapshots of the last 120 days. Tapes cycle to off-site and allow us to go back to quarters, annuals, etc... [which isn't optional, you are pretty much legally obligated to have that].
In my opinion, that drastically raises the cost of keeping backups on disk and I am still a big fan of tape based backups, but a well maintained raid array should be equally reliable IMO.
Disagree with the reduction in the "cost of keeping backups" [if we are just comparing technologies]. Online archival is expensive - you are constantly paying for power and cooling. And power required by the number of drives required for an adequate archival system is not trivial. It is however worth the convenience as it reduces the *labor* of retrieval from archive - and labor is always the most expensive component of any system.
fyi: at our office, we actually do keep a lot of data sitting on powered off disks, but we also make tape backups we send offsite of the same data. We've had about 10 hard drives fail in the last year. ie. when we pulled the drives off the shelf and tried to use them,
Our experiments had the same result: archival to cold disks is a terrible strategy.
they would not work reliably. None of the tapes we have retrieved from offsite have failed. Our offsite tapes are mostly a combination of LTO-1 and LTO-3.
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