Disclaimer: my experience with tapes is dated. I used IBM tapes with a mainframe (System 390, library robot and all) until 1995, and then only used consumer level myself, but had witnessed the occasional horror story at a client's.

> Well I've recently restored 150 LTO-2 tapes from 2002/2003 using a perfectly current LTO-4 drive, and I'm pretty sure you'd have a heck of a hard time successfully reading all of a bunch of 150 hard drives of the same vintage without losing a single file.

That might be true. However, I have so far had perfect success with about 50 or so drives that I've restored from (across 10 years or so), and abysmal success with tapes (about 1/10 in the mainframe days would not restore).

> Hard drives are much less reliable than tapes; hard drives aren't made to be stored on shelves;

That's true, but neither are tapes. Hard drives are less tolerant to environmental conditions than tapes, they survive better when exposed to heat, and get damaged more quickly when exposed to cold (oils used to keep it running smooth tend to congeal irreversibly when exposed to cold for long). Also, at least in the past, even weak magnetic fields wreaked havoc on tapes, and even strong ones spared drives.

> As soon as your storage and archival needs are more than a few disk drives, do yourself a service and switch either to RDX or to tape. Storing basic HDD on shelves is a recipe for data loss. I know it because we sell backup solutions to people doing it and losing data all the time :)

In my current top-secret venture, I need to keep everything (~20TB/customer) randomly accessible for 3 years, and cold-store accessible or 7. So far, we just keep multiple copies (some online and some offline), and keep refershing to newer larger drives every couple of years. When I specced it 3 years ago, tapes were twice as expensive (I need a tape drive at every customer location + at least two at my office) and didn't properly address the random access aspect.

But I keep re-evaluating. So far, the next step seems to be going to a BackBlaze style pod - which would also address the valid drive-fails-completely concern you raised.

p.s., I find the "compressed" statistics really misleading. Every kind of backup software can compress - if I saw a hard drive manufacturer sell a ("2TB drive (1TB uncompressed)" I would consider it fraudulent, but that's the standard for tapes. For the record, my data is (as far as tape drives are concerned) not compressible at all -- think audio, video, jpegs, and other analog recordings.

EDIT: p.p.s: Of course, don't keep hard drives on shelves. Nor tapes. Humidity and temperature need to be controlled, and the environment needs to be anti-static. For archival purposes, the 5400-RPM usb self-powered disks are a little slow, but keep very well, in my experience, with reasonable temp/humidity.

EDIT2: (bad) memories are coming back. The biggest problem I recall with tapes in the mainframe days, were that some tapes (the daily and weekly backup sets) were continuously reused, to the point that mechanical wear and tear was a bigger problem than magnetic wear. And the even bigger problem was that you only found that out when trying to restore. One advantage of disks is that you keep reading them while writing them - wear is apparent much more quickly. If you're only doing archives and never rewrite tapes, that doesn't matter. If you keep reusing the same tapes/disks, it makes a huge difference in reliability.