The optical storage surprise
Remember when Amazon Web Services (AWS) announced Glacier, a data archiving service, almost 2 years ago? It offered long-term, slow-retrieval (3-5 hours) storage for the then unheard of price of 1¢/GB while promising to maintain several copies across geographies.
Pretty amazing. A little less amazing today now that disk prices are reaching 3¢/GB, but there's still power, cooling, mounting and drive replacement costs to consider in addition to those multiple copies.
At first many assumed that Amazon was using tape. But the couple of remaining tape robot vendors haven't shown any unusual signs of life and there were some denials. Plus the long-term storage requirements for tape require a level of climate control that large data centers may not support.
So it wasn't tape.
Then the general estimate was that Amazon must be using disk. Perhaps the new Shingled Magnetic Recording (SMR) drives that, in theory, could double existing drive density at the cost of expensive rewrites.
Seagate admitted they'd sold a million SMR drives - and it wasn't through NewEgg. WD is getting on board with SMR as well.
The plot thickens
But if Glacier's data was stored on disks - even spun down disks - why the tape-like 3-5 hour retrieval delay? Disk drive robots?
No. Disks are sensitive to physical handling. I've never seen an HDD handling robot or the Zero-Insertion Force drive connector that would be required to minimize physical shock.
One more thing: all current tape libraries are designed to handle ≈200 gram tapes, not 600+ gram 3.5" HDDs. 2.5" drives are ≈100 grams, and have much better shock and vibe specs, but there hasn't been even a whisper of SMR notebook drives, plus the economics are much worse.
The Storage Bits take
Therefore, by a process of elimination, Glacier must be using optical disks. And not just any optical discs, but triple or quad-layer Blu-ray discs.
Not single discs either, but the otherwise inexplicable Panasonic 12 disc cartridge shown at this year's Storage Visions conference. That's 1.2TB in a small, stable cartridge with RAID so a disc can fail and the data can still be read.
For several years I didn't see how optical disk technology could survive without consumer support. But its use by major cloud services explains its continued existence.
Comments welcome, of course. There's more evidence for this theory, but I'll spare you.