TEST BENCH AND PROTOCOL
In testing the Micron P320h HHHL PCIe SSD, well be using our Enterprise Test System.
Well be using Red Hat Enterprise Linux and/or CentOS for most all of our enterprise testing. Linux has less overhead and is generally more flexible when it comes to evaluating performance.
That said, our enterprise test bench is OS agnostic. Well apply a few new standardized testing techniques in addition to some of our older test protocols. We want to isolate and explore the individual performance of the review drives as accurately as we can.
As the test bench evolves, we hope the result is a more tangible, relevant performance evaluation.
CAPACITY AND R.A.I.N.
As we stated earlier, the P320h’s 1024GB of flash gets used in different ways. 128GB, or 12.5%, goes to R.A.I.N.— Micron’s NAND-level redundancy scheme. Should one NAND device fail prematurely, the R.A.I.N. system should keep the drive operating though the Micron parity scheme (at the expense of 1/8th of the drive’s flash). After that, 197GB is used for over-provisioning and 50GB goes to spare area (~7%).
All told, that leaves just about 650GB available capacity.
Micron’s R.A.I.N. (redundant array of independent NAND) system is similar to other systems. For every 7 elements of NAND, one additional unit goes to parity. In the event of a failure, the drive can seamlessly recover the data of the failed NAND from the parity data. There are other schemes that could be used, but the 7 +1 method offers the best combination of speed and capacity.
R.A.I.N. takes blocks from different bits of flash, and groups them into “super blocks” composed of eight individual blocks. One of these blocks is used to store parity data for the other 7 blocks, which is enough to recover one of the remaining seven individual blocks. At a global level, it’s enough to recover should a whole die fail in service. Whole die failures aren’t the most common cause of drive failure (that dubious distinction probably belongs to firmware issues), but they happen frequently enough that using 1/8th of the flash on a drive for protection makes sense.