"And I agree to the other commenter, unplug the HDDs and they will cost just as much as the tapes in that climate-controlled shelf."
Exactly. The WHOLE ARTICLE assumes your disk-based archive is live. As a matter of fact, from the article:
"trashed data was "snapshotted", replicated etc, propagating the original fault. Fortunately for users: "To protect your information from these unusual bugs, we also back it up to tape. Since the tapes are offline, they’re protected from such software bugs."
I would argue that hard disks can be taken offline, and thus be protected as well. The difficulty here is Google does redundancy to protect from failure (think RAID). This is NOT a "backup" or "archive." Google seems to carry a few days worth of snapshots on live disks, as is alluded by them saying the corruption was spread over a few days of snapshots.... But they had to fall back to their offline storage to find the good data. Since most need for restores happen within the first 24hrs of the data loss (some can stretch that out to 3 days), Google is actually doing a good job here. They protect the most common window with live snapshots: easy to restore. The less-likely-to-be-needed old data is stuffed onto tapes.
As for more in the HDD vs Tape comments:
"How much is this 48-tape loader again? Because the HDD headers and logic board are included in the drive price, not just the magnetic disk. The fair comparison becomes 48 drives adding up to 35Tb versus a fully loaded tape interface. Now tape wins."
1TB HDDs run in the range of $55USD each. Bump that to 2TB and you're looking about $70USD each. With an 800GB LTO4 tape running $35USD ($70 for 2 totaling 1.6TB), it becomes a bit clearer. Now we factor in the drive: a Quantum LTO4 drive for $1,600USD. You could likely pick up a 48-slot NEO400S used for just under $10,000. Of course, you could accomplish the same with 24 2TB HDDs as a JBOD (2x 12 drive racks perhaps?) A HP StorageWorks M6412A with a FiberChannel connection would do. You can get a refurb for $1,121USD (refurb because the 48 tape library was priced as "used"). Now, you can complain that the disks need to be stuffed in the hot swap cases to slot into the array, and yes, you're right. So much more hassle than just stuffing a tape in. But what do you get in return? A FiberChannel connection to your JBOD (two of them actually), which would be faster than SCSI Ultra320 I reckon. HDDs in JBOD would be equivalent to tapes with in an archive (since you'll need to sequentially number both if you use some software to write data across them). Of course, with HDDs, you could do any number of backup options. Tapes, you only have one: use a program to write data to it sequentially. HDDs can just be NTFS with raw files, whole disk encrypted, or a 1:1 partition dupe of your server's disk drive.
What does tape have going for it? The best thing I can come up with is "industry support." Most backup programs are designed with tape being the eventual end-point. Only recently have D2D2T or D2D2D been popular options. Oh, and a note about readability and just "finding" an old tape drive to read your data: you still need the disk drive to actually work. You need the connectors to use it (Ultra2 SCSI anyone?), and be able to actually install your backup software. Depending on your solution, many of those things can be eliminated with disk. I have no problem finding an ATA66 (very old hard drive)-capable connector. You can get one that converts an ATA disk into a USB drive for <$20USD. I doubt even a dusty used tape drive can be had for that cheap. I'm sure SATA will be in the same boat come another 10-20yrs.