In a recent compilation, the fine folks at Storage Newsletter compiled annual disk drive shipment into a bar chart. The bad news: disk drive unit shipments peaked almost a decade ago, in 2010.
The good news: the industry still shipped more than 375 million disk drives in 2018, as many as it did in 2005.
What killed the disk drive?
That's easy: the solid state drive, or SSD.
SSDs have rapid access times, under a millisecond, compared to ≈10ms for disks. As a bonus, they can handle thousands of IOPS, as opposed to perhaps a couple of hundred IOPS for a disk. And they are a little more reliable, especially in notebooks.
What's keeping the disk drive alive?
That's harder. One is price: disks are down to as low as 2 cents per gigabyte, compared to 25 cents per gig for SSDs.
Another is, counter-intuitively, performance. If you're moving large files, such as videos, a group of striped disk drives will give you multiple gigabytes per second of bandwidth. And if you need to move that much data, the 2 cents per gig cost makes a real difference.
Then there's capacity. You can buy a 10-12TB disk for a few hundred dollars. While there are large SSDs, they're costly, intended for enterprise use, not consumers.
But probably the biggest factor keeping disk drives alive is the cloud. Those massive data centers are stocked with upwards of a million disks each. While cloud suppliers use SSDs as well, for most services pooled disk drives are both economical and fast enough.
Recent innovations like the helium drives from HGST and, later, Seagate, are aimed at cloud providers and the enterprise. They offer lower power consumption and greater capacity, both important when you're running millions of drives.
Whither the disk?
Since pundits have been predicting the demise of tape for decades - and it hasn't happened - disks too will stick around for decades to come due to the same factor that keeps tape alive: cost.
Despite the shrinking market, tape vendors keep improving tape capacity, performance, and cost for their remaining customers who use tape for their deep archives. Disks are a much bigger business and several hundred million units a year still justifies significant R&D.
The Storage Bits take
I still use about a dozen disks in addition to several SSDs. And I do have a sentimental attachment to the technology, as silly as that may seem, because the technology is magnificent and the industry's cost efficiency has fueled the computer industry for decades.
When I joined the industry in 1981, after years as a computer hobbiest, disk drives cost as much as $80,000 per gigabyte, and offered truly pathetic performance on the order of 50 IOPS, 2MB/sec bandwidth, and, maybe, a 25,000 hour MTBF. You get better specs today on a USB thumb drive.
But in the intervening years that $80,000/GB has become 2 cents/GB, with much higher performance, reliability, and power and space efficiency. Disk drives are incredible devices, but they've moved off the center stage for PC applications.
In turn, SSDs are threatened by newer technologies, such as non-volatile RAM. I doubt flash-based SSDs will have anywhere near the 60+ year market lifespan of disks.
Courteous comments welcome, of course.