Intel Optane SSD 905P: Why It's So Special
As we've mentioned on a few occasions in the past, 3D XPoint is being positioned as a revolutionary, non-volatile memory tier that can offer significantly better performance than NAND flash memory, but with DRAM-like access times. 3D XPoint also offers higher endurance than traditional NAND flash memory, but with similar capability to scale in density. Our original coverage of the 3D XPoint announcement is available here if you’d like a quick refresher.
The Optane SSD 9050P resembles some of Intel’s previous PCIe-based NVMe add-in cards, but it is a different animal altogether. Although the SSD 905P may look like any other HHHL NVMe drive, everything from its controller to its storage media is different.
The specifications listed on the previous page hint at some of those differences. The drive’s throughput doesn’t seem terribly impressive versus other enthusiast-class, NVMe storage products, but note that its 4K IOPS ratings, with fully random and mixed 70/30 workloads, are recorded at low queue depths. Most NAND SSDs quote random IOPs scores at high queue depths, which don't occur very often during day-to-day use cases. Like the Optane SSD 900P that came before it, the new SSD 905P shines at low queue depths, where NAND flash-based storage products typically stumble. The drive’s endurance is also rather high -- at 10 full drive writes per day, we're talking many Petabytes of data written before there's anything to be concerned about from an endurance standpoint.
Differences Between 3D XPoint And NANDIntel Optane drives based on 3D XPoint media don't require over-provisioning like NAND-based SSDs either. The random write performance of a NAND-based SSD can be improved by increasing the amount of spare storage capacity, because it makes defragmentation more efficient. Since 3D XPoint memory is write-in-place media, there is no defragmentation needed, and therefore no performance to be gained by over-provisioning. Some spare space is used to store ECC and metadata to maintain low error rates throughout the life of the drive, but Optane drives are not over-provisioned in the same way as NAND.
We should also note that there are significant differences in the actual 3D XPoint media versus NAND. For example, NAND features lots of extra capacity inside every die for sparing out blocks, as well as managing ECC code words. 3D XPoint memory media does not have or even require the extra capacity, so that type of over-provisioning doesn't really apply. With that said, spare capacity beyond the user defined area is leveraged for ECC, firmware, and other maintenance operations.
The Intel Optane SSD 905P also handles requests differently than NAND SSDs. For example, when a read request comes into the drive, the normal read write paths are always in hardware, which exploits the low latency performance characteristics of the media. In addition, one read of 4KB is now spread across multiple channels and dies. With NAND-based SSDs today, 4KB reads usually leverage only a single channel. With Optane, the aggregate performance of multiple channels and dies being utilized for small data requests results in higher realized performance. There is also no need to perform defrag operations with 3D XPoint, so the combination of write-in-place media and firmware tuned for these characteristics results in consistently low overall latency, in the neighborhood of 10 microseconds, in addition to higher quality of service (QoS).
Optane drives like the Intel Optane SSD 905P also offer consistent performance when in a steady-state, loaded up with data. Whereas NAND-based solid state drives tend to offer best performance fresh out of the box (FOB), once they've been filled with data and written / re-written, etc. performance drops off. This doesn't happen with Optane -- the drives offer consistent performance regardless.
What this means in the "real world" is that a system outfitted with an Optane SSD will remain more responsive, more often, versus a NAND-based SSD, when there's heavier, concurrent workloads that may be taxing the storage sub-system. Anyone that's felt their system slow down when downloading a few torrents and moving files on some NAND-based SSDs, will appreciate the consistency and QoS offered by Optane.