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Intel gives hard drives a boost with Optane Memory


Taking another crack at storage caching
— 11:00 AM on March 27, 2017

Intel's Optane SSD DC P4800X and its underlying 3D Xpoint memory technology seem poised to bridge a performance gap between NAND density and DRAM performance in certain types of datacenter workloads, but that $1520 device isn't meant for the average PC builder in the least. Intel still has ambitions for Optane in client PCs, but competing with NAND SSDs on both a speed and capacity basis would prove prohibitively expensive given Optane's roughly $4-per-gigabyte cost right now. Instead, Intel is taking a different tack for the moment: improving the performance of hard-drive-only systems for a reasonable cost.

The company says that people considering desktop PCs want three things above all: performance, security, and storage capacity. Right now, hard drives tick the capacity box, but anybody who's used an SSD knows that spinning rust doesn't perform anything like flash. Hard drives still make up the vast majority of storage devices shipping in today's PCs, however, and Intel anticipates that'll continue to be the case for the foreseeable future.

Enter Optane Memory. Intel's first client Optane product uses a hardware-and-software stack that purports to cache a user's most commonly accessed files on a fast slice of PCIe 3.0 x4-connected storage. Its reliance on newer tech aside, Optane Memory as a whole sounds similar in principle to what Apple does with its Fusion Drive-equipped iMacs. It also sounds similar in principle to Intel's own Turbo Memory technology, a small slice of NAND on a riser card that did basically nothing for system performance when it debuted in some notebooks back in 2005. Given Intel's history with elaborate solid-state caching layers, I was skeptical about the prospects of another take on the idea. Optane has some fundamental differences that promise a better showing this time around, however.

For one, Optane doesn't need a large number of dies to achieve maximum performance like most NAND devices do, so one Optane die (as one will find on Intel's 16GB Optane Memory device) or two dies (as found on the 32GB gumstick) should offer enough parallelism to deliver a performance increase over devices with small amounts of NAND on board, like SSHDs. Even more importantly, Optane Memory devices enjoy the same class of high QD1 performance that the SSD DC P4800X does, so they can offer maximum performance at the low queue depths typical of desktop workloads.

For its part, Intel thinks Optane Memory will boost system responsiveness above all—the major beef with hard-drive-only PCs. Using the Sysmark benchmarking suite, the company claims only minor increases in application performance, but the suite's responsiveness test comes away with twice the performance of a system with a hard drive alone.

To bolster the point that QD1 performance matters most for desktop users and that Optane is ideally suited to boosting system responsiveness, Intel shared some internal data about the read and write queue depths for the synthetic PCMark Vantage benchmark and some demo workloads from its labs.

Intel also performed trace analysis for the launch performance demands of several commonly-used applications one might find in the typical workplace.

Finally, Intel collected application traces from a number of its employees' PCs to show the queue depth demands of more productivity-focused workloads.

The point of these graphs is clear: most random desktop workloads level off at about QD4, and the majority of accesses happen at QD1 or QD2. Given those characteristics, Optane Memory seems ideally suited to speed up application launches and perhaps to lessen the wait for commonly-accessed files, at least so long as those accesses are primarily random. Presuming that's the case, Optane Memory seems much better poised to offer some kind of speedup to a user's commonly-used applications than a small NAND cache like Turbo Memory might have.

Optane Memory isn't much good without its companion software, an unobtrusive utility that sits in the system tray. Intel says this application will render the Optane cache transparent to the user experience. The only storage device that should show up with an Optane Memory system is the user's primary system drive (along with any other non-Optane Memory storage devices that may be installed). There's a lot of black-boxiness to how the app's caching algorithm works, but Intel suggests Optane Memory won't be caching entire applications like games on the Optane device itself, simply because they'd often be too large to fit in 16GB or 32GB of space. Instead, I got the impression that the Optane Memory app will look for common files (like shared libraries and operating system files) that are often accessed by many programs and cache those instead.