Intel's Caching History

Intel's first attempt at using solid-state memory for caching in consumer systems was the Intel Turbo Memory, a mini-PCIe card with 1GB of flash to be used by the then-new Windows Vista features Ready Drive and Ready Boost. Promoted as part of the Intel Centrino platform, Turbo Memory was more or less a complete failure. The cache it provided was far too small and too slow—sequential writes in particular were much slower than a hard drive. Applications were seldom significantly faster, though in systems short on RAM, Turbo Memory made swapping less painfully slow. Battery life could sometimes be extended by allowing the hard drive to spend more time spun down in idle. Overall, most OEMs were not interested in adding more than $100 to a system for Turbo Memory.

Intel's next attempt at caching came as SSDs were moving into the mainstream consumer market. The Z68 chipset for Sandy Bridge processors added Smart Response Technology (SRT), a SSD caching mode for Intel's Rapid Storage Technology (RST) drivers. SRT could be used with any SATA SSD but cache sizes were limited to 64GB. Intel produced the SSD 311 and later SSD 313 with low capacity but relatively high performance SLC NAND flash as caching-optimized SSDs. These SSDs started at $100 and had to compete against MLC SSDs that offered multiple times the capacity for the same price—enough that the MLC SSDs were starting to become reasonable options for every general-purpose storage without any hard drive.

Smart Response Technology worked as advertised but was very unpopular with OEMs, and it didn't really catch on as an aftermarket upgrade among enthusiasts. The rapidly dropping prices and increasing capacities of SSDs made all-flash configurations more and more affordable, while SSD caching still required extra work to set up and small cache sizes meant heavy users would still frequently experience uncached application launches and file loads.

Intel's caching solution for Optane Memory is not simply a re-use of the existing Smart Response Technology caching feature of their Rapid Storage Technology drivers. It relies on the same NVMe remapping feature added to Skylake chipsets to support NVMe RAID, but the caching algorithms are tuned for Optane. The Optane Memory software can be downloaded and installed separately without including the rest of the RST features.

Optane Memory caching has quite a few restrictions: it is only supported with Kaby Lake processors and it requires a 200-series chipset or a HM175, QM175 or CM238 mobile chipset. Only Core i3, i5 and i7 processors are supported; Celeron and Pentium parts are excluded. Windows 10 64-bit is the only supported operating system. The Optane Memory module must be installed in a M.2 slot that connects to PCIe lanes provided by the chipset, and some motherboards will also have M.2 slots that do not support Optane Caching or RST RAID. The drive being cached must be SATA, not NVMe, and only the boot volume can be cached. Lastly, the motherboard firmware must have Optane Memory support to boot the cached volume. Motherboards that have the necessary firmware features will feature a UEFI tool to unpair the Optane Memory cache device from the backing device being cached, but this can also be performed with the Windows software.

Many of these restrictions are arbitrary and software enforced. The only genuine hardware requirement seems to be a Skylake 100-series or later chipset. The release notes for the final production release of the Optane Memory and RST drivers even includes in the list of fixed issues the removal of the ability to enable Optane caching with a non-Optane NVMe cache device, and the ability to turn on Optane caching with a Skylake processor in a 200-series motherboard. Don't be surprised if these drivers get hacked to provide Optane caching on any Skylake system that can do NVMe RAID with Intel RST.

Intel's latest caching solution is not being pitched as a way of increasing performance in high-end systems; for that, they'll have full-size Optane SSDs for the prosumer market later this year. Instead, Optane Memory is intended to provide a boost for systems that still rely on a mechanical hard drive. It can be used to cache access to a SATA SSD or hybrid drive, but don't expect any OEMs to ship such a configuration—it won't be cost-effective. The goal of Optane Memory is to bring hard drive systems up to SSD levels of performance for a modest extra cost and without sacrificing total capacity.

Introduction Testing Optane Memory
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  • romrunning - Monday, April 24, 2017 - link

    Speaking of real-world tests, I am waiting for SQL Server tests on an Optane SSD - like on that DC P4800X. The "enterprise" review of the 4800 was all synthetic benchmarks with some disclaimer that they can't simulate all enterprise loads. Sure, you can't simulate everything, but I'm very disappointed that -nothing- enterprise level was even tested.
  • ddriver - Monday, April 24, 2017 - link

    I am sure it is just an unfortunate coincidence, and it is not like intel is trying to hide the actuality of real world performance :)
  • darkfalz - Monday, April 24, 2017 - link

    SSD cache / Hybrid SSD drives work okay on certain workloads, mainly productivity stuff, but if you have a lot of games/media they tend to fill up really quickly and I don't think any of the companies that write the algorithms, Intel included, can really figure out how reliably and over long usage periods decide what should be in the cache and what shouldn't.

    I have a 24GB SSD cache (ExpressCache) in my Notebook and I partitioned the OS/Programmes for to one partition, and put all the media on the second partition, and set it to only cache the first partition. This setup works pretty well.

    I also have a Hybrid SSHD in another laptop (only 8GB I think) that I mostly use as a background downloading PC, and after a few days of doing this any useful boot / OS / Chrome stuff that was in the cache has been evicted and it's back to booting at the same speed as a regular HDD.

    Nice in theory, highly variable in practice. I never tried the Intel SRT out because larger SSD affordability improved a lot after it was released.
  • satai - Monday, April 24, 2017 - link

    Can I just put it into a PCIe slot (via a reduction), boot linux from an other SSD drive and use it as any other block device?
  • romrunning - Monday, April 24, 2017 - link

    Per the article: "However, the Optane Memory can also be treated as a small and fast NVMe SSD, because all of the work to enable its caching role is performed in software or by the PCH on the motherboard. 32GB is even (barely) enough to be used as a Windows boot drive, though doing so would not be useful for most consumers."
  • DigitalFreak - Monday, April 24, 2017 - link

    Are you also going to test Intel SRT with a ~$77 SATA SSD and the same WD HDD? I bet it would perform about the same, and SRT works with non-boot drives.
  • eddieobscurant - Monday, April 24, 2017 - link

    How about using the same test setup as with the other ssds and run the same benchmarks for comparison?

    I get you wanna please intel for giving you access to optane (which should be named remote preview by the way) , but come on !!!

    Also the new graphs ( probably suggested from intel , since tomshardware has something like these ) are not easy to understand with a quick look.
  • Billy Tallis - Monday, April 24, 2017 - link

    These two Optane reviews interrupted my work on putting together a new 2017 consumer SSD test suite to replace our aging 2015 suite. When the new test suite is ready, you'll get comparisons against the broad range of SSDs that you're used to seeing and more polished presentation of the data.
  • Shadowmaster625 - Monday, April 24, 2017 - link

    Can this be used as a boot drive?
  • romrunning - Monday, April 24, 2017 - link

    Per the article: "However, the Optane Memory can also be treated as a small and fast NVMe SSD, because all of the work to enable its caching role is performed in software or by the PCH on the motherboard. 32GB is even (barely) enough to be used as a Windows boot drive, though doing so would not be useful for most consumers."

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