Direct flash is a red herring

With a broad portfolio of performance flash, capacity flash, and hybrid flash arrays, NetApp is the second-largest provider of enterprise flash array storage worldwide, and we’re currently innovating at the fastest pace in the company’s 33-year history. The design tenets for this flash portfolio include a common storage OS, NetApp^® ONTAP^®, and state-of-the-art SSD technology. Our customers gain an infrastructure that enables simplicity at scale, consistent performance, leading data security features, ransomware protection, and integrated recovery workflows, across all enterprise workloads, on the edge, in the data center, and in the cloud. 

NetApp has been shipping flash systems for more than a decade and has partnered with tier 1 global SSD manufacturers to incorporate advanced technologies into its enterprise flash systems. The aim is to invest in research and development that support customers' business goals rather than to seek attention by announcing the largest capacity drives.

Pure Storage has been increasing their claims about the supposed design advantages they enjoy by using direct flash rather than SSDs. Their claims include better power consumption, better density, better reliability, and even better performance. We want to set the record straight.

We know that a growing part of your opex budget is the cost of data center power and cooling. Pure has made bold claims about power savings, but their claims are inaccurate. NetApp platform engineering has visibility into the power consumption tables from all major flash component vendors, and we don’t see any power efficiency advantages in using direct flash compared to SSDs.

Pure continues to claim that their systems draw less power than “the competition,” while never stating who that competition is or what side-by-side comparison was made. Clearly, Pure didn't test against NetApp systems.

Side-by-side comparisons of Pure and NetApp storage arrays, based on published data, show that Pure systems consume more power. The result is greater CO2 emissions and higher ongoing operating costs.

How can this be? Well, when Pure makes their claims, they prefer to compare the power consumption of their DirectFlash Modules (DFMs) to that of an SSD. Obviously, this isn’t a relevant comparison. Customers purchase and deploy complete storage arrays, not just DFMs or SSDs. So comparing power draw per system is a more relevant indicator of sustainability. Pure systems consume a larger amount of power to perform flash management tasks using the system controller’s CPU. By contrast, NetApp systems handle these tasks more efficiently within the SSD. Direct flash requires that all operations related to the flash translation layer (FTL)—garbage collection and flash management—are performed by the operating environment. NetApp SSD-based arrays do not require CPU-level cycles to manage those operations. Each SSD has memory and processors to perform maintenance operations so that flash wear is protected and referenced data cells are available for writes. Because these operations are performed by the SSDs rather than by the system CPU, performance overhead on the array is greatly reduced.

NetApp uses SSDs because they allow the storage array controllers to focus on providing consistent performance to your applications. Pure claims that using system CPU to perform flash management tasks gives their systems an advantage over SSD-based systems. They fail to mention that their use of direct flash means that their storage controller CPUs need to work harder, performing garbage collection and other flash management tasks, which causes inconsistent application performance.

To follow the previous point, in an SSD-based array, the storage controller doesn’t have to manage these flash management tasks. It can be dedicated to what it should be doing—delivering high, consistent performance and data services. This is a significant advantage of NetApp systems.

Can Pure flash management tasks be programmed to run in the background to minimize the impact on system performance? Yes, but… the point when a system requires sustained maximum performance is precisely when flash management tasks become critical and must run in the foreground. This creates interference with workload I/O performance and often causes severe latency spikes. In other words, stressing the array and demanding consistently high performance means that eventually performance degrades.

If consistent high performance is important for you, choose SSD-based storage.

As data centers fill up and the cost of building new data centers rises, capacity density is becoming more crucial. Some Pure DFMs have more capacity than SSDs, but they are also physically larger. They take up more space. Let’s look at the real-world comparisons.

A comparison of flash capacity per rack unit between currently shipping NetApp and Pure models shows no density advantage for direct flash modules. Pure is shipping similar flash components to what NetApp is shipping in their SSDs. So let’s look at the number of flash media devices each vendor packs into a rack unit. The Pure FlashArray//X line can fit 20 DirectFlash Modules into its 3RU base chassis. Pure FlashBlade can hold up to 40 DFMs in its 5RU chassis. The NetApp 2RU ASA and AFF models hold 24 SSDs, and the 4RU models hold 48 SSDs. Devices per rack unit has a direct correlation to capacity per rack.

Pure recently stated that their flash modules are experiencing annual failure rates of 0.15%, which may not sound like a bad number. (Additionally, they claimed that this is a small fraction of what competitors experience. They don’t say where that data comes from.) NetApp’s currently shipping NVMe SSDs are experiencing failure rates that trend at or below this annual failure rate.  There’s no advantage to Pure’s custom flash modules. Consider that tier 1 SSDs are thoroughly tested by dozens of storage vendors and hyperscalers before release.

NetApp ONTAP arrays provide two levels of data encryption, making them inherently more secure than arrays relying on direct flash that have no hardware encryption. Customers can choose self-encrypting SSDs for encryption at the device level and simultaneously take advantage of ONTAP systemwide software data encryption. This is part of the reason that NetApp arrays garner industrywide data security certifications that other vendors don’t have, and contributes to our ability to claim that we deliver the most secure storage on the planet.

The bottom line is that NetApp doesn’t see direct flash as a factor providing business advantages in power consumption, performance, capacity, and density. We also see customer benefits in using SSDs for better reliability and data security. Perhaps that’s why the world's leading storage vendors and most public cloud workloads use SSDs. Of course there are corner cases, but the exceptions only prove the rule.

NetApp continuously evaluates the trade-offs between building systems with industry-standard SSDs versus custom flash module, and today we don’t see advantages to direct flash modules in power, density, reliability, or performance. Regardless of Pure’s claims in these four areas, they have never proven to the market the superiority of DirectFlash Modules.

NetApp is not a component vendor; we are a systems vendor focused on providing business benefits to our customers. By leveraging the SSD feature set, NetApp can invest more engineering resources to simplify data estate management and provide the richest set of services for data protection, security, privacy, and governance.