Spectrum Virtualize, FlashSystem and SCMs

ORIGINALLY POSTED 13th July 2018

7,785 views on developerworks

Its been great to see all the interest over the last week on the new FlashSystem 9100 products announced on July 10th. Interesting too on the register with the battlecard information, and some of the usual ‘anonymous’ comments that seem to miss the point – particularly that we have 3 flash families. In reality its just 2, with V and A families, where V9000 is surpassed in many ways by the new FS9100, but we’ve chosen to drop the V from the name. Anyway, haters will hate, lovers will love, but one thing that I have seen a few comments and questions about is SCM, or Storage Class Memory capability.

In my post on Tuesday I hinted that the FS9100 products have been designed from the ground up with NVMe and SCM in mind. For those that don’t know what SCM is, think of it as the next generation of solid state storage devices, where just as Flash SSD’s came along just over 10 years ago and shook up the HDD market, so SCM’s will come along in the not too distant future and add yet another leap in latency – or more to the point leap in latency reduction.

At present there are two main SCM’s out there. Intel and Micron have been shipping Optane drives, typically in the M2 and PCIe card formats using their 3D X-point technology. This gives us an order of magnitude reduction in latency, so think 10us vs 100us from Flash at best – similarly Samsung have their Z-NAND, or I believe what they are now calling Z-SSD which is in the same ball-park in terms of latency.

Now, when SSD first came along the price was prohibitively expensive, which is when things like EasyTier came along. Add 5% or such capacity of SSD, and let the heat define what data ends up using the ‘accelerated’ storage. Well, the same thing is going to be true for SCMs. They are not, and will not be cheap, we have become spoilt now, as NAND based SSD are much cheaper now than they were, and are a viable option for an all-flash solution. SCM’s wont be there for some time, its really taken NAND about 8-10 years to get to that position. So how would we best make use of SCM?

Well, threefold, at least. Obviously having a small amount in an EasyTier configuration, with a new Tier00 if you like. That would give the same kind of benefit as a hybrid configuration of Flash and HDD today. But now we’d be maybe using Tier00 SCM, Tier0/1 Flash and maybe if you have a need for online archive data NL-SAS. HDD’s are still here!

The second use case is as an acceleration device, where the storage system sees fit. So in a way, let us use them to help accelerate the system itself. One logical use case is meta-data, so for example de-duplication, the more signatures and hash information you can keep in memory, the less you need to page from disk, or maintain in DRAM. Getting meta-data operations down to 10us, vs the 100us+ from the backend, means the meta-data I/O amplification can be greatly ‘hidden’ and so accelerate data reduction technologies closer to non-data reduced performance – when meta-data misses occur.

A third use case would again be slightly selfish on the storage controller side, if we could replace a big chunk of the DRAM in the system with NV SCM technology, then we could almost do away with battery backup etc – it may even work out cheaper to have large SCM caches onboard, rather than DRAM caches. But this will require system planer and CPU changes, such as ways to hold up the onboard CPU caches in the event of a power loss…

Anyway, these are just some ramblings, and to let everyone know, yes for sure we are looking at these ideas, and have plans to make use of SCM with NVMe, and the FlashSystem9100 was designed with this in mind. And as you all know, the Spectrum Virtualize software model is so flexible (celebrating its 15th birthday back in June) and has shown it can keep up with sweeping changes like this before…  So keep your eyes and ears peeled for future announcements in this area.

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