IEEE report: When it comes to SSD and HDD tech roadmaps, money talks – Blocks and Files

An IEEE report sees no mass takeover of the disk drive market by SSDs because HDD cost/bit is decreasing fast enough to prevent SSDs catching up.

The International Roadmap for Devices and Systems 2023 Update (IRDS) is discussed in Tom Coughlin’s August Digital Storage Technology Newsletter (subscription details here.) It covers many mass storage technologies: SCM, NAND/SSDs, HDDS, tape and emerging memories including DNA.

We’re focusing on SSDs and disk drives here and the IEEE report notes that HDDs have ceded the fast data access market to SSDs: “As flash-based SSD costs have fallen, HDDs have been displaced: first in consumer PCs, and increasingly in data centers, as SSDs have come to occupy the tier of frequently, and randomly, accessed data.”

Nowadays: “HDDs are used for bulk mass storage and SSDs are used for speed. Frequently requested and typically randomly accessed data resides in the SSDs, while less-frequently used and typically sequentially accessed data is kept in high-capacity HDDs. “

However: “SSDs and HDDs continue to coexist because HDDs (and tape) will continue to offer the lowest cost per bit for the foreseeable future.”

As a consequence: “Today the HDD market continues its decline in unit volume primarily due to displacement by solid state drives.” The IEEE report sees total HDD unit ships increasing from 2023 to 2028 as the nearline mass storage market increases in size:

The mobile, branded, consumer electronics and retail HDD markets continue to decline over this period, or so the forecast states.

SSD capacity is increasing as layer counts in 3D NAND increase and drive down the cost/bit, but the rate of increase is slowing. This is because adding layers also adds cost. The alternative way of increasing capacity, adding bits to cells, has reached a possibly temporary wall with QLC (4bits/cell) as the next 5bits/cell; level – penta-level cell or PLC – has such short endurance as to make infeasible, for now.

The IEEE report has a table from its IRDS (International Roadmap for Devices and Systems) community showing NAND chip density progression out to 2029:

IRDS does not commit itself to saying QLC will displace TLC from 2025 onwards, instead using the term TLC+. We are currently just entering the high 200s layer count area with Micron’s 276-layer technology with a 1Tb die.

The table shows 300+ layers in the 2027 period and 500+ in the 2029 timeframe, leading to a doubling in maximum die capacity from 2TB in 2025, to 4Tb in 2027 and 8Tb in 2029.

Despite this capacity increase, SSD cost/bit will not become equal to or go below HDD cost/bit, the report states: “The ultra-high capacity HDD market will remain unavailable to flash for the foreseeable future due to its lower cost per bit.”

No alternative semiconductor-based memory technologies, either volatile or non-volatile, will replace NAND or DRAM. Keeping the fate of Intel’s Optane mind, this is because their performance and other characteristics do not justify a supplier bearing the cost of ramping production to a volume level where the cost/bit, performance, endurance and power consumption means customers will switch from either DRAM or NAND.

Technologies like ReRAM, MRAM, etc. will remain niche embedded market alternatives because of this restriction.

HDDs will increase their capacity, and therefore lower their cost/bit as a table indicates:

All the suppliers – Seagate, Toshiba and Western Digital – will move to HAMR technology, and use patterned heated dot media in the 2037 period:

The report states: “Patterned media has discrete elements of the magnetic material distributed in an orderly fashion across the disk surface. These patterned dots become the magnetic bits when the head writes on them. Patterned media will be combined with HAMR recording to create 10 Tb/in2 magnetic recording areal density within the next 15 years.”

One enduring HDD issue is access density; IO operations per second per byte. The report says: “As the storage capacity on a surface increases, the time it takes to access a given piece of data increases and the time to read or write all the data on the disk increases as well. Although the average performance of disk drives to access data is increasing by about 10 percent per year … the disk access density (Access density = I/Os per second per gigabyte) of disk drives is continually decreasing as disk drive capacity increases faster than disk drive performance.”

Despite advances such as multi-actuator technology, access density will continue to decline as HDD capacity increases. NAND caching, as with WD’s OptiNAND technology, can help mitigate this.

Altogether the IEEE report makes for fascinating reading and there is much more information in its 117 pages than we can cover here. It is a terrific primer and introduction into current and future mass data storage technologies.