Horses, Automobiles and SSD Form Factors

Can you imagine the traffic jams if all of today's roads were as wide as they were when horse-drawn carriages were a main mode of transportation? Even worse, picture the chaos if both horse-drawn carriages and automobiles had to share the roads now. Crazy, right?

Just as it would be absurd to mix horse-drawn carriages with modern cars on today’s roads, the tech industry faces a similar dilemma with storage technology. A transition is happening today from hard disk drives (HDDs) to solid state drives (SSDs) in data centers. If it sounds ridiculous to intermix horse-drawn carriages and modern automobiles on today’s highways, is it not just as ludicrous for the computer industry to use arcane form factors meant for the old mechanical discs for today’s blazing-fast SSDs? 

The ongoing AI craze is further turbocharging this transition. Allowing legacy form factors in this hyper growth environment is akin to not just cars but ultra-fast, clean burning EVs getting gummed up with the old horse-drawn carriage and its refuse!

The Small Form Factor Technical Affiliate (SFF-TA), a technical working group of the Storage Networking Industry Association (SNIA), specified the Enterprise and Datacenter SSD Form Factor (EDSFF) E1 and E3 form factors for modern SSDs several years ago.

Within EDSFF, the E1.S form factor offers several key benefits over traditional form factors for SSDs in data center environments. The fundamental difference is that E1.S was designed with the NAND geometry in mind. It breaks free from the limitations of disc geometries that the 2.5” and derivative form factors were designed to accommodate.

• Flexibility in Design: The E1.S specification features many different size options, and they all use the same PCB length and connector. This means compatibility is a non-issue. The only difference between the versions is the heatsink size, which allows them to output different levels of performance. For example, for use cases like a high-capacity boot drive or for general use, the E1.S 9.5mm would be an ideal solution, whereas the 15mm variant is the preferable solution for higher workload use cases. Conversely, the 25mm variant may be the preferred solution where environmental power is limited, whereas a 5.9mm, 9.5mm or 15mm version may be better for a situation with adequate cooling.
• Improved Thermal Management: The E1.S design provides better surface area and airflow for heat dissipation compared to standard 2.5" drives. This allows for higher power consumption and performance without overheating issues, thus providing a higher IOPS/Watt solution.
• Performance Density: When an application needs storage capacity and bandwidth, a smaller drive that can deliver both is better to deliver higher IOPS/TB. Due to the fact that many more E1.S SSDs can be connected in the same chassis compared to standard drives, the application is able to access data at a higher density.
• Performance Scaling: E1.S SSDs can support from 12W for a bare PCB to 25W of power for the heat sink-enabled solution. This targeted power budget enables E1.S SSDs to saturate the PCIe^®0 x4 bandwidth for increased performance and optimize for performance scaling at the same time.
• Higher Density in 1U Servers: The compact E1.S form factor allows for packing significantly more drives (up to 36-64) into a 1U server chassis, compared to just 10-12 standard drives, thereby increasing storage density.

So, you may be wondering – why is the 2.5” form factor still in use? There are still many use cases requiring a mixed-use scenario of both HDDs and SSDs in the same chassis to accommodate a mixed workload. Also, 2.5” 15mm allows for higher capacities with dual PCBs - which E1.S can’t match today. In those scenarios, the 2.5” form factor HDD and SSD is a suitable solution and the E1.S may not be an optimum solution.  

For the flash-only data centers rapidly gaining traction in AI and Machine Learning applications, there's little reason—aside from industry inertia—to continue using traditional drives and form factors. EDSFF provides a range of solutions tailored to specific use cases. In summary, the E1.S specification addresses the limitations of standard SSDs in areas like thermal dissipation, performance scaling, and storage density - making it well-suited for the demanding requirements of modern hyperscale data centers. 

Maybe we should rename the legacy HDD a "Horse-Drawn Drive" before consigning it to the annals of history! 

PCIe is a registered trademark of PCI-SIG.

mm refers to thickness.

2.5-inch indicates the form factor of the SSD and not its physical size.

IOPS: Input Output Per Second (or the number of I/O operations per second)