Western Digital is introducing a new high-end enterprise NVMe SSD, the Ultrastar DC SN840, and a NVMe over Fabrics 2U JBOF using up to 24 of these SSDs.

The Ultrastar DC SN840 uses the same 96L TLC and in-house SSD controller as the SN640, but the SN840 offers more features, performance and endurance to serve a higher market segment than the more mainstream SN640. The SN840 uses a 15mm thick U.2 form factor compared to 7mm U.2 (and M.2 and EDSFF options) for the SN640, which allows the SN840 to handle much higher power levels and to accommodate higher drive capacities in the U.2 form factor. The controller is still a PCIe 3 design so peak sequential read performance is barely faster than the SN640, but the rest of the performance metrics are much faster than the SN640: random reads now saturate the PCIe 3 x4 link and write performance is much higher across the board. Power consumption can reach 25W, but the SN840 provides a range of configurable power states to limit it to as little as 11W.

Western Digital Ultrastar DC
Enterprise NVMe SSD Specifications
  Ultrastar DC SN840 Ultrastar DC SN640
(U.2 variant)
Ultrastar DC SN340
Form Factor 2.5" 15mm U.2 2.5" 7mm U.2 2.5" 7mm U.2
Interface PCIe 3 x4
or x2+x2 dual-port
PCIe 3 x4 PCIe 3 x4
NAND Flash Western Digital 96L BiCS4 3D TLC
1.92 TB
3.84 TB
7.68 TB
15.36 TB

1.6 TB
3.2 TB
6.4 TB
960 GB
1.92 TB
3.84 TB
7.68 TB
800 GB
1.6 TB
3.2 TB
6.4 TB

3.84 TB
7.68 TB
Write Endurance 1 DWPD 3 DWPD 0.8 DWPD 2 DWPD 0.3 DWPD
Sequential Read 3.3 GB/s 3.1 GB/s 3.1 GB/s
Sequential Write 3.1 GB/s 3.2 GB/s 2 GB/s 1.4 GB/s
Random Read IOPS 780k 472k 473k 429k
Random Write IOPS 160k 257k 65k 116k 7k (32kB writes)
Random 70/30 Mixed IOPS 401k 503k 194k 307k 139k (32kB writes)
Active Power 25 W 12 W 6.5 W
Warranty 5 years

The SN840 supports dual-port PCIe operation for high availability, a standard feature for SAS drives but usually only found on enterprise NVMe SSDs that are top of the line or special-purpose models. Other enterprise-oriented features include optional self-encrypting drive capability and support for configuring up to 128 NVMe namespaces.

The SN840 will be available in two endurance tiers, rated for 1 drive write per day (DWPD) and 3 DWPD—fairly standard, but a step up from the 0.8 DWPD and 2 DWPD tiers offered by the SN640. The high-endurance tier will offer capacities from 1.6 TB to 6.4 TB, while the lower-endurance tier has slightly higher usable capacities at each level, and adds a 15.36 TB capacity at the top. (The SN640 is due to get a 15.36 TB option in the EDSFF form factor only.)

Between the SN840, SN640 and SN340, Western Digital's enterprise NVMe SSDs now cover a wide range of use cases, all with their latest 96L 3D TLC NAND and in-house controller designs. Shipments of the SN840 begin in July.

OpenFlex Data24 NVMe Over Fabrics JBOF

Using the new Ultrastar DC SN840 drives, Western Digital is also introducing a new product to its OpenFlex family of NVMe over Fabrics products. The OpenFlex Data24 is a fairly simple Ethernet-attached 2U JBOF enclosure supporting up to 24 SSDs (368TB total). These drives are connected through a PCIe switch fabric to up to six ports of 100Gb Ethernet, provided by RapidFlex NVMeoF controllers that were developed by recent WDC acquisition Kazan Networks. The OpenFlex Data24 is a much more standard-looking JBOF design than the existing 3U OpenFlex F3100 that packs its storage in 10 modules with a proprietary form factor; the Data24 also has a shorter depth to fit into more common rack sizes. The OpenFlex Data24 will also be slightly cheaper and much faster than their Ultrastar 2U24 SAS JBOF solution.

The OpenFlex Data24 will launch this fall.

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  • ballsystemlord - Wednesday, June 24, 2020 - link

    So what is the limit on the amount of power drives can pull over the SATA HDD connector?
    I mean, how much more could future models draw?
  • Billy Tallis - Wednesday, June 24, 2020 - link

    The connectors are rated for 1.5A per pin and have 3 pins for 12V, so these drives are pulling less than half of the connector's limit. Heat dissipation is a bigger challenge for U.2 than power delivery. (M.2 makes power delivery difficult because it only supplies 3.3V, and supplying 2.5+A of that with less than 5% voltage drop often requires putting the voltage regulators pretty close to the slots.)
  • back2future - Wednesday, June 24, 2020 - link

    system temp (from up to 25W for several devices, and that's on pcie3 nowadays) on connectors should stay (far) below 185F (85C) for guaranteed endurance of connecting contact resistance below 15mR, AFAIK
  • back2future - Thursday, June 25, 2020 - link

    sorry, means could add upto additional 15mR (to connection resistance on a 30mR level for each pin)
  • eek2121 - Tuesday, June 30, 2020 - link

    Somewhat unrelated rant: The m.2 standard sucks and we need to go back to 2.5”/3.5” drives. This can be done without sacrificing speeds. There was a demonstration recently that showed PCIE 4 speeds being maintained for 12 meters.

    m.2 takes away from motherboard real estate on consumer devices, has limited real estate itself, and can be tricky to cool properly since you can only place a heatsink on one side of the drive.

    Returning to a 2.5” form factor fixes all of these issues and as a bonus allows for a backplane to be plugged into an x32 or x16 slot to easily allow drive hotswap.
  • James5mith - Wednesday, June 24, 2020 - link

    Wow, with the depth of those drive caddies and the weird single tiny connector, it looks like they might be using a backplane that could also be used in a 1U "ruler"/EDSFF style enclosure.
  • Billy Tallis - Wednesday, June 24, 2020 - link

    That's what it looks like to me, but WD didn't want to comment on that during our briefing. An EDSFF style backplane should be good for airflow whether or not it matches any of the standard EDSFF form factors. (Looks closest to the 2U 3" Long 16.8mm thick variant, which certainly isn't going to be the most popular EDSFF form factor for SSDs.)
  • ksec - Wednesday, June 24, 2020 - link

    Very interested in the SN340 as HDD replacement. I wonder how much would it cost.
  • Santoval - Wednesday, June 24, 2020 - link

    Do you have a motherboard with a U.2 slot? First start with that..
  • Kakti - Thursday, June 25, 2020 - link

    Just have to buy a PCIe to U.2 adapter card. $30 on Amazon, only requires x4 slot

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