Analyst Coughlin Associates’ latest Digital Storage Technology Newsletter sees no signs that SSDs are going to stop new hard disk drive (HDD) sales after 2028.
All-flash array vendor Pure Storage is at the forefront of predictions that there will be no new HDD sales from that timeframe onewards. CEO Charles Giancarlo said in June 2023: “The days of hard disks are coming to an end – we predict that there will be no new hard disks sold in 5 years.”
Thomas Coughlin, President of Coughlin Associates, issues his DST newsletter each quarter and the May 2024 issue contains historical disk units and capacity shipped information with projections of current trends.
The market watcher plotted a chart that shows HDD annual unit shipments since 2001 by market sector;

From 2010 onwards there has been a dramatic decline in units shipped as market sectors like smartphones, consumer electronics and 10K rpm enterprise 2.5-inch mission-critical storage replaced disk drives with faster and smaller flash drives. The SSDs cannibalised the HDDs. Yet from 2018 onwards mass capacity nearline HDDs, the 3.5-inch form factor (7,200 rpm drives) became increasingly popular for storing secondary data; data that was not mission-critical.
By 2024 this accounted for more than half of all HDD shipments and Coughlin projects them to take more than 75 percent heading out to 2029. A projection which looks at disk form factors shows the same picture:

The vey small 1.8-inch form factor drives stopped being made years ago, and the 2.5 inch 10K drives, which accounted for more than half the drives shipped in 2011, now represent around a quarter and that proportion will shrink further as we progress to the end of the decade, according to Coughlins Associates.
However, and after a multi-year decline, the total number of disk units shipped are expected to rise from 2025 onwards because the 3.5 inch form factor drives, the nearline ones, will sell in greater numbers.
Their relatively slow ascension is accompanied by a dramatic rise in the capacity shipped as their areal density – the terabytes stored per platter – increases due to technologies such as HAMR, says the analyst:

The capacity shipped curve increased at a steep angle from 2023 as hyperscaler buyers started to store vastly more unstructured data to fuel social media, general enterprise and AI-specific unstructured data, files and objects.
This trend is forecast to send the average $/GB for HDDs consistently downwards, crossing $0.01/GB in 2024 and continuing is decline out to 2029, estimates Coughlins Associates. The net effect of this disk price per GB drop and capacity rise on tape and SSD sales is that the disk share of total tape+SSD+HDD storage capacity shipped is expected to rise and rise steeply as we progress to 2029:

The SSD proportion rises but at nowhere near the rate of the disk expansion, according to Coughlin Associates. It appears from these HDD capacity, form factor and unit ship charts that the analyst doesn’t agree with Pure Storage’s assertion that no new HDDs will be sold after 2028.
Asked about this, Coughlin told us: “Yes that is my assessment. … SSDs will, in my opinion, not be competitive to HDDs for secondary storage with HAMR and other HDD announcements.”