Optane SSD's value lies in latency as NVMe limits full IOPs potential.
TORONTO — Much of the potential of 3D Xpoint technology is expected to come from the DIMM form factor, but Dell-EMC is bullish enough on the Intel Optane SSDs to include it in its latest PowerMax storage array, which also boasts end-to-end NVMe.
The company’s updates to PowerMax introduce storage class memory (SCM) as persistent storage via dual-port Intel Optane SSDs. In a telephone interview with EE Times, Caitlin Gordon, vice president of product marketing at Dell-EMC, said the dual-ported drive provides built-in resiliency for the storage platform, and reflects a close collaboration with Intel.
The key value proposition for PowerMax with dual-port Intel Optane SSDs is latency, she said. “This is all about achieving the right response times out of the drive.” Those response times have been achieved in the lab for some time, and as a lead development partner, Dell-EMC’s focus has been on getting the resiliency of the firmware to where it needs to be, said Gordon.
The combination of NVMe and SCM in the PowerMax array offers as much as 50 percent better response times compared with SAS and flash — while delivering up to 15 million IOPS, 350 GB/sec throughput, and better than 100 microseconds of read latency. But as much as PowerMax has been geared toward delivering low latency, she said it remains to be seen how much the IOPs of Intel Optane SSDs can be improved — as Optane-based storage to date has only leveraged the technology as a single-ported drive acting as a cache. “If you’re only using it for cache, the benefits are pretty limited (especially depending on the architecture of the storage array). We really haven’t seen what Optane can provide.”
Dell-EMC’s latest PowerMax arrays combine Intel Optane SSDs with end-to-end NVMe (including NVMe-oF cards) while optimizing their PowerPath multipathing software which leverages Connectrix switches. (Source: Dell-EMC)
These latest PowerMax arrays aren’t using Optane as a cache. Rather, said Gordon, they’re deployed in the same drive tray as the NVMe-based flash drives and are being used in a persistent manner for user data. In addition, they are leveraging machine intelligence to decide which information can benefit most from being on Optane, she said, rather than requiring an administrator to make that decision. “To ask human intelligence to figure out what data should be on which drive type continuously over the system’s life is not something realistically customers can nor should be doing,” she said. “That’s why PowerMax has a real-time machine learning engine built in. It’s all designed to optimize for performance without adding any burden on the storage chain.”
While Dell may be bullish on Optane SSDs, Jim Handy, principal analyst with Objective Analysis, said they’ve not really lived up to expectations when compared to flash-based SSDs. “Everybody was expecting a thousand times performance increase and ended up only getting seven to eight times.” Although the IOPs aren’t that good, he said, the latency is, which is hugely important to the hyperscalers.
The SSD iteration of Optane may also have a relatively short shelf life as DIMM availability becomes more widespread, Handy said. Right now, however, DIMMs are as rare as hen’s teeth — with speculation that technical issues are delaying widespread availability. “Not only that, but the Optane DIMM only works with a few Intel CPUs that have been designed with the DDR-T bus that Intel created for the technology,” he said. “In a year, all of that will be different.”
Once Optane DIMMs start shipping in volume, there are going to be a lot of people who look at the Optane SSD and the Optane DIMM, which costs the same per gigabyte, and wonder why they would buy the slower SSDs when they get the DIMM for the same price, said Handy. “Once the Optane DIMM becomes widely available and once processor support for the DDR-T bus becomes widespread then I would expect Optane SSD unit volume to start to decline.”
Optane SSDs are also hamstrung by the NVMe interface — much like how flash SSDs couldn’t realize their full potential on IDE and later, SATA. While NVMe unlocked the performance of flash, it’s unlikely there will be an interface specifically designed for Optane SSDs, said Handy, as Intel is content with NVMe for SSDs and DDR-T for DIMMs. “The XPoint chip itself is roaring fast, but when it has to go through all the handshaking that’s in NVMe, it slows it down.”
Beyond the inclusion of Optane, Dell-EMC’s latest PowerMax arrays build on last year’s predecessors, which had NVMe-based flash drives and were ready for NVMe-over Fabric (NVMe-oF) with the inclusion of new 32GB Fibre Channel and NVMe-oF cards. The arrays’ PowerPath multipathing software has also been optimized for an end-to-end NVMe environment and is leveraging Connectrix switches.