Western Digital is one of the most vocal proponents of the Zoned Namespaces (ZNS) storage initiative, so it is not surprising that the company this week became the first SSD maker to start sampling of a ZNS SSD. When used properly, the Ultrastar DC ZN540 drive can replace up to four conventional SSDs, provide higher performance and improve quality of service (QoS).
ZNS SSDs have a number of advantages over traditional block-based SSDs. For one, they place data sequentially into zones and have better control over write amplification, since the software 'knows' what it is dealing with. This means that ZNS SSDs don't need as much overprovisioning as traditional enterprise drives. Many enterprise drives rated for 3DWPD (drive writes per day) reserve up to 28% of their raw capacity for overprovisioning. ZNS needing as little as a tenth of that significantly increases usable SSD capacity.
Second, since ZNS manages large zones rather than a bunch of 4KB blocks and doesn't need to perform garbage collection as often as traditional SSDs, it also improves real-world read and write performance.
Finally, ZNS substantially reduces DRAM requirements.
Western Digital's Ultrastar DC ZN540 SSD is based on the company's own dual-port NVMe 1.3c-compliant controller, as well as 96-layer 3D TLC NAND memory. The controller fully supports ZNS Command Set 1.0 specification, and the drive is ready to be deployed by companies running software that supports Zoned Namespaces. The drives come in an industry-standard U.2 form-factor, so they're drop-in compatible with existing servers.
ZNS promises to be particularly useful for hard drives based on shingled magnetic recording (SMR) technology, as well as SSDs powered by 3D QLC NAND. Note that since 3D QLC NAND yet has to gain traction in the datacenter, Western Digital decided to use proven 3D TLC memory.
Western Digital claims that because of all the advantages that ZNS brings to SSDs, the Ultrastar DC ZN540 and its successors increase drive utilization and reduce total cost of ownership (TCO), which is something every operator of a datacenter cares about.
Right now, the Ultrastar DC ZN540 is sampling with select customers only, so to a large degree this is a test vehicle. It remains to be seen whether these drives will ever be deployed more broadly.