What We’ve Learned Over the Years
Several years ago, one of our OEM customers asked if we could squeeze a 2.5” SATA HDD into a high reliability, high durability 9.0mm optical disk drive form factor for laptops. That meant creating a device the size of a DVD drive that could withstand the punishment of tens of thousands mate-demate cycles. After a little consideration I replied, “Yeah, I think we can do that.” CRU Engineering had years and years of experience developing durable, high reliability removable SATA storage products so this was just an extreme miniaturization of what we already were doing. We called it the DataPort DP27 and it became a great and popular product for CRU. Cool.
A couple years later the engineering team asked how small we could make an M.2 PCIe NVMe removable drive. It again had to be durable, highly reliable, and fit into a 9.0mm optical disk drive form factor and run at PCIe speeds (3200MB/s vs. 600MB/s for SATA). After a day of sticking a few virtual parts together I replied, “Yeah, I think we can do that.” We had some experience with M.2 and U.2 NVMe PCIe drives so it was not completely unknown territory. Still, it is amazing how optimistic one can be when embarking into the unknown.
CRU cut its teeth on IDE and SCSI technologies and easily migrated to SATA when that became the new standard. With PCIe solid state memory becoming more popular and sure to be ubiquitous, it was an obvious path of development. Our OEM customers are also focusing on smaller computers all the time, which means fewer accessible storage drive bays. At the same time, customers continue to demand removable storage for data security, off-site storage, transfer of large data sets, and mass content distribution. We are also receiving requests for smaller, lighter, faster, and more versatile removables. A palm-sized M.2 module was an obvious solution to those needs.
Finding the Right Solution
Unlike the auto industry that (or at least seems to) starts with a swoopy enclosure and then tries to fit people and power plants into that space, our design process is to define the critical components and then place them within the industry standard volume. What we call the “docking connector” was the first component to research. It had to support PCIe data rates of 3200MB/s, measure less than 8mm tall, have enough contacts to connect x4 PCIe from the M.2 plus ancillary lines, and have a high mate-demate life. Nothing on the market answered all our needs so we focused on a particular family of connectors and then performed expanded mate-demate tests to validate the applicability. After 100,000 cycles with no failures – that’s right, we really tested that many cycles – we moved ahead with the design.
The second design hurdle was heat. Although PCIe M.2 modules are “low power,” their surface area is small so the power density is quite high. The single controller chip tends to be the hotspot that must be addressed. If a PCIe M.2 module gets too hot, it will throttle its performance to control the temperature. We knew this was a non-starter, especially because our customers demand high performance. Therefore, the enclosure must also be a heat sink.
The base clock for PCIe is 100MHz. Managing these high–speed PCIe signals from the M.2 through the docking connector to the host interconnect, through the cable to the native host interconnect or host bus adapter is quite a task. Great care must be employed during PCB routing, cable design, and selection of the interconnects to maintain signal integrity. Once a design is realized in hardware, it must be qualified by a certified lab to the PCIe specifications prior to final release.
Of course, from an engineer’s perspective everyone wants everything. One of the things at the top of everyone’s list is the ability to hot-swap. However, PCIe was meant to be an internal communications protocol for static architectures; it was not originally conceived for removables. Although our products are designed with hot-swap in mind, the host computer’s BIOS and OS have to do the heavy lifting in order to get true hot-swap to work. Every time a system boots, it enumerates the memory and must be aware if any of it is removed and replaced in order to enumerate again and be recognized by the host. But that is another story for another day!
With all these design requirements and goals, we developed a very small, removable PCIe module. In fact, it is so small we used the code name Gumstick while developing it. At just 9mm x 44.4mm x 103.5mm, the SHIPS – or Secure High Performance Storage – module has become the cornerstone of our PCIe ecosystem. Because it’s predominately aluminum it is also very rugged, and populated with today’s 8TB storage, it screams at 3200MBPS. Pretty cool for a pocket-sized removeable.
Senior Mechanical Engineer