Incorrect Comparision
"The real underlying question again is why choose only one?"
Exactly. The best bet to be fully protected would be to use a combination of the two. After all, how much is your data really worth?
However, I do agree the comparison is highly unfit for purpose:
"You have to get to the airport two hours before the flight, undergo a lengthy security check, face cabin baggage restrictions or wait at the hold baggage carousel the other end, and then get from your arrival airport to your actual destination, adding time and cost."
Unless the "two hours before the flight" part is disk formatting, not much else applies here. Backup Exec (as much as I dislike parts of it) will do D2D2D without much hassle, do compression on the fly, and encrypt the results as well. Should handle the "baggage carousel" and "security check" parts just dandy. A bit of proper solutions, and you can eliminate the "arrive two hours early" bit by scripting a format on first use.
Now, why use tape over disk? One can suggest cost. However, I just picked up some 1.5TB HDDs (external, USB) for $70. 1.5TB of tape would be ~$55 as two LTO4 800GB tapes, or ~$74 as a single LTO5 tape. So no, price isn't really a comparison point, especially when you factor in a 24/48 tape rack unit or stand-alone tape drive. Even a JBOD 24 disk rack costs less than a 24 tape rack. The key point is, the disk drives are quite reliable when not in use. Every time I hear discussion of "hard disk backups," everyone automatically assumes "live and spinning" drives. This may be a good idea for your standard backup target. However, for archiving, the disks do not need to be continually plugged in. My "archived" drives have a grand total of 10 "on" hours. Just 10. Granted I'm only in charge of ~500GB of actual data (minus the VM images, ISOs, etc). The pleasant thing about my drives (being of the 1TB or 1.5TB variety), I store more than just a "month end" on my "archived" drives. They actually have a backup from early in the month (perhaps the 8th) as well as mid-prior month (about the 17th). Therefore, if my previous month-end drive is unreadable for ANY reason (including getting lost, damaged, eaten, or otherwise destroyed), I can snag data from the next-best point in time (likely the 8th of the following month) from the next-month's drive. Tape can do with with appending data to the end of the backup set, so it's not a "big" selling point. However, doing this EASILY is the advantage of disks. You can't simply delete a backup set from tape by deleting a folder and writing new data; you'd have to purge the whole tape if your data set started before an appended dataset.
Lifespan. It's a moot point. Companies should be doing D2D or T2T data refreshes at least every 3-5yrs. Depending on storage conditions, the readability of either disk or tape in this case should be the same: just fine. The hard disk platters aren't going to be geomagnetically zeroed, nor is the tape. Granted, bringing tapes or drives from storage for their "refresh" cycle does incur a risk of accident. Which would fair better sitting on the shelf for a full 10 years? Well, tape has made strides in the resiliency of the magnetic ribbon the data is stored on, but I personally wouldn't trust it past 10 years. I've read articles written about a company's "data viability" checks, which have found that their tapes aren't very readable (20% in one case) after 8 years or so in "ideal" storage. But that was 4 years ago or more, meaning at least 12-yr-old tape tech.
Honestly, the best reason I can think of for using disks is rapid recovery. You don't have to read in an archive manifest and find your way to the data you need, then spend the tape seek-time recovering it. Depending on your disk-drive backup method, you may even be able to use OS tools (such as full-text search) to help you find the data you need. Very rarely when I'm asked to recover something does the person know the date it was deleted or the name of the file. They tell me "a few months ago" and "it has this in the text" (for Word docs for instance). A very simple "file contains" search in windows will find it on a "raw files" backup (what you'd see with a copy/paste of a folder tree). You simply can't do this with a tape. You'd have to restore your whole dataset and then search through it.
For those still insistent on tapes, you likely have a tape library and other robotic or automated tools, hence your investment keeps you tied to the technology. D2D2T is always an option, and a rather good one in my opinion. However, depending on your know-how, you can set up a D2D2D system that can be worlds better than simply using that middle "D" as a landing space to be promptly shuffled off to tape oblivion. My middle "D" solution holds a 6-month rotating archive on-site, with about 120 days of rotating daily snapshots, all while still spawning off month-ends to the final "D" for offsite storage. I've only once had to grab our off-site storage backups due to this. It was to fetch a file nearly 2 years old, and the best guess they had was "it was in my files over a year ago." Took us hooking up 3 USB hard drives (we tried at 1.5yrs and second was at 2yrs, third was for the "most recent" copy at about 1.75yrs), and about a 30min full-text search for the first drive. File was recovered after about an hour of returning with the offsite backup disks.
Biting the hand that feeds IT
