Micron's 32-Channel Controller Simplifies PCIe-Based SSDs
Micron set out to simplify PCI Express-based SSDs with its P320h. But before we can understand how the company does this, let's first have a look at a more conventional layout. The image below corresponds to Intel's SSD 910.
Starting from the PCI Express connector on the left, you have a RAID/HBA chip attached to a number of SAS- or SATA-enabled controllers. Those controllers, in turn, communicate with the NAND. In essence, you're taking a number of SSDs (in the example above, four), hooking them up to a host bus adapter, and presenting them as a single device.
In contrast, the P320h consists of a PCI Express interface, a host controller with the ability to communicate over PCI Express built-in, and the flash memory. When you take the HBA out of the equation, you alleviate bandwidth limitations and minimize latency.
Clearly, that custom ASIC is responsible for enabling Micron's design. The company partnered with IDT (Integrated Device Technology) to develop the P320h's controller, combining its extensive knowledge of NAND with IDT's leadership in high-speed serial switching. The result is a 32-channel (!) controller built into a 1517-pin FCBGA (Flip Chip Ball Grid Array) package.
Let that sink in for a second. Most of the controllers you find in SATA-based SSDs communicate across eight channels. It makes sense, then, that it'd take a quartet of "eight-channel SSDs" on a PCI Express-based add-in card to saturate the interface. Micron makes it very clear that its P320h loves workloads that push high queue depths, and we can see the drive's controller was designed to shoulder those intense environments. As a matter of fact, company representatives recommended that we test using queue depths at least as high as 256.
As any hardware geek can tell you, there's something about a bare circuit board that begs for examination, and the P320h's layout is incredibly clean. This half-height, half-length (HHHL) PCI Express 2.1 card is about as elegant as it gets, consisting of the passively-cooled controller flanked by NAND flash and DDR3 cache.
The Micron/IDT controller sits front and center. Immediately to its left are five Micron 256 MB DDR3-1333 memory packages, with another four around back, totaling 2.25 GB of cache. Additionally, the PCB hosts 32 NAND packages, each with 16 GB of Micron's 34 nm ONFi 2.1 single-level cell memory. There is also a pair of double-sided mezzanine boards, adding 32 more packages. All told, the 700 GB RealSSD P320h hosts 1 TB of SLC NAND.
The 32-channel controller, the 2.25 GB of cache, and the 1 TB of SLC memory should all be clear indicators that this thing is an enterprise-class piece of equipment designed for enterprise-class workloads. Fortunately, we have some of those to throw at it.