Hard disk shipments dropped 10% QoQ, 2% YoY

This jives very well with what I’ve observed. Decreasing demand for enterprise storage hard disks, or as I call them “Spinning Rust Drives” (or SRD) as compared with SSD (Solid State Drives).
The summary is here with a key quote being

3.5″/2.5″ Enterprise HDDs: For a second consecutive quarter, total enterprise HDD sales declined. Both performance enterprise and nearline HDD volumes were down for the quarter, as
total unit shipments fell to approximately 16-17 million.

Again, jives well with what I’ve observed.
Mellanox has a good take on its blog, noting that

Flash keeps taking over
Every year, for the past four years, has been ?The Year Flash Takes Over? and every year flash owns a growing minority of storage capacity and spend, but it?s still in the minority. 2017 is not the year flash surpasses disk in spending or capacity ? there?s simply not enough NAND fab capacity yet, but it is the year all-flash arrays go mainstream. SSDs are now growing in capacity faster than HDDs (15TB SSD recently announced) and every storage vendor offers an all-flash flavor. New forms of 3D NAND are lowering price/TB on one side to compete with high capacity disks while persistent memory technologies like 3D-XPoint (while not actually buillt on NAND flash) are increasing SSD performance even further above that of disk. HDDs will still dominate low price, high-capacity storage for some years, but are rapidly becoming a niche technology.

This is a critical point. While SRD are dropping in volume, there is not enough SSD fab capacity to supply the market demand. Which, curiously, means that economics 101 is strong and we see a healthy supply/demand curve in play. Moreover, entry into this market (e.g. building fabs for NAND) is prohibitively expensive. This means that the SSD supply will be constrained for the foreseeable future.
This also opens the way up to other mass producable technologies. Given the contenders to replace NAND for SSD, I’d argue that the combination of the least expensive and most easily licensed/reproduced system (which might be NAND) will be the high growth bit for a while.
Apart from that fab entry cost.
Without reading the tea leaves too hard, it is pretty clear that SRD are headed in the direction of archives, and colder storage. Tape is still around for now, though, I am not sure if anyone will be looking at it in 2-5 years time frame … serialized storage technologies that don’t do reasonable jobs on seeky loads might not fare well.
Possibly SSD/Tape hybrids, with the SSD providing not really a cache per se, but a fractional capacity tier, and many parallel tape drives providing some semblence of many heads on a disk … but the issue then is that seek times to new “sectors” takes 102 to 103 seconds, as compared to a hard disk, where seeking is around 10-2 seconds. Thats 4 to 5 orders of magnitude difference, and for active archives, I can’t imagine a potentially non-serial workload being deployed on such a device.
Even backups … you have the storage bandwidth wall (SBW) problem, where you have a small pipe bandwidth relative to your capacity. SBW measures time to move an amount of data.
$SBW = Capacity / Bandwidth$
1PB of data, at 100 MB/s (about the real writing rate of tapes) is about 107 seconds, or 1/3 of a year. Do you really want that for your read/write cycle? Even 10 units running in parallel for 1GB/s is 1/30 of a year, or about 12 days. And your data keeps growing.
No, tape has a limited lifetime going forward IMO. Pipe size (the B) is one of the major issues, seek rate being the other. Low cost doesn’t matter if you can’t get your data off of it fast enough when you need to.
What I think I see going forward is people basically “sloshing” their data between storage systems, with HDD playing a large role going forward. Larger denser HDD could make integrating archive and backup fairly simple into an all flash storage system. Not as tiers (data motion is your enemy, as it reduces the usable value of Bandwidth in the SBW equation).
So I expect a long tail on the HDD. They won’t go away any time soon. Well, not all of them. 10k and 15k RPM drives are probably done for.