What’s happening with NVMe and SATA?

As NVMe is approaching SATA pricing, it delivers massive performance benefits for a marginal added cost, with significantly higher IOPS and lower latency which vastly improves the efficiency and TCOS of your system.

Here are some of the key insights:


  • “NVMe is the path forward”
  • “A cost-effective solution to displace SATA once and for all”
  • “There’s simply no reason to stay on SATA SSDs for data storage”
  • “Great gateway drive to get users off prior-generation storage and onto NVMe-based flash”

NVMe delivers outstanding performance and consistent quality of service:

  • “SATA drive quickly ran out of steam”
  • “Outstandingly low latency……consistent quality of service”
  • “Outstanding performance through a wide range of IOPS”

The drive that we will be looking at in this article is the Western Digital Ultrastar DC SN640 NVMe SSD. It is the successor to the Ultrastar DC SN630 with key improvements in performance. Both drives use Western Digital’s in-house NVMe controllers with their own NAND and firmware which provide massive optimizations leading to consistent low latencies and high performance. These drives are for mainstream designs, which is the drive that Western Digital markets as a transitional drive to get enterprise customers away from last-gen SATA/SAS Flash storage technologies and into current NVMe Flash storage.

When NVMe™ drives first came out, we knew the performance would be superior, but questioned when they would be cost comparable to SATA SSDs. Due to their initial cost, NVMe drives were used for enterprise applications that needed to take advantage of their high-performance characteristics. It didn’t take very long for NVMe drives to become cheaper than SATA/SAS SSDs in terms of dollars-per-IOPS. But now, we are starting to reach the point where they are not that much more expensive than SATA/SAS SSDs on a capacity basis. This GB vs. dollar comparison was driven home to us when we received the Western Digital Ultrastar® DC SN640 NVMe SSD in the lab for performance testing – it offers dramatic performance improvements over SATA/SAS SSDs and targets the mainstream enterprise storage market. Now that NVMe SSDs are near cost parity, we see them as a replacement for SATA drives in the data center for mainstream applications as they offer better performance while having lower power requirements. Before digging into the specifics of the Ultrastar SN640, and giving an overview of the performance testing that we did on it, let’s first take a look at Western Digital’s background with, and current lineup of, Flash storage, as well as the technology behind the SN640 that makes it such an attractive replacement to SATA/SAS drives.

NVMe drives have been in the enterprise market for a while now, and the biggest blocker to their widespread utilization has traditionally been their cost, but this is no longer the case. The street price of an SN640 with a capacity of 7.68TB is $1,400, and a comparable SATA SSD comes in at $1,200. A lower-capacity drive, such as the SN640 960GB, comes in at $300, while a comparable datacenter-rated SATA SSD drive is priced at $260. In other words – for about a 16% increase in price, you get a far more performant drive. By switching to NVMe drives servers can handle modern workloads which demand fast response times. SATA drives, with their limited bandwidth and much higher latencies, cannot efficiently handle the demanding storage requirements of today’s applications.

Due to their high price, NVMe drives were relegated to niche use cases when they were initially released. Now, however, newer NVMe SSDs like the SN640 has become a storage solution for mainstream workloads, such as backing for virtual machines (VMs), serving as the Flash cache for software-defined storage (SDS), and even acting as boot devices. The one drawback that we currently believe is impeding their more widespread adoption is that servers are still struggling to catch up with them, and not all servers can support the number of NVMe ports that people would like to populate them with. If this is indeed the case, then server architects need to use this valuable resource judicially (not from a cost standpoint, but from a performance standpoint) and make sure that their performance is used as wisely as possible.

The SATA drive’s latency degraded rapidly to the point where it took ~3 milliseconds to respond while the SN640 soldiered on with a gradual rise in latency up to just over 500 microseconds until we stopped the testing at slightly over 150,000 IOPS.

Our testing on the Ultrastar DC SN640 confirmed that Western Digital has delivered a mainstream NVMe SSD which balances performance and power for a cost-effective solution to displace SATA once and for all. NVMe drives quickly achieved parity in cost per IOPS and we predicted that there would be an inflection point where they would be cost-competitive on a capacity basis in the future, and we are now at that point. In a casual price comparison, we found that there was only a slight uplift in the price of the SN640 over SATA/SAS SSDs on a per GB basis. When viewed through the performance lens, there’s simply no reason to be using SATA SSDs for data storage.

Western Digital has long been an innovator in, and at the forefront of, storage technology – and this achievement extends to flash drives. Western Digital’s relentless innovation can be seen in their SN640 line of drives where they were able to use their technical prowess to not only extract superior performance from the device but to do so at a very attractive price point.

View available SSD from Matrix Warehouse.

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