Dual-Mode Enterprise SSD
Enterprise SSD brand DapuStor revealed a new dual-mode configuration for its J5060 enterprise drive that combines single-level cell and quad-level cell flash on a single drive. The drive’s new firmware runs selected QLC cells in a faster pseudo-SLC mode, trading capacity for speed.
As an example, the 30.72TB model trades around 4TB of QLC for 800GB of pSLC, a ratio closer to 5:1 than 4:1. The other two configurations put aside 400GB or 1.2TB with a cost between 6% and 20% of the QLC capacity. No dedicated SLC NAND is required, as this uses a software-defined media configuration, DapuStor said. The drive still lacks pricing, a named customer, and a general availability date.
Performance and Endurance
Typical consumer QLC drives have a pSLC cache that fills with fast performance, with data later transferring over to QLC. However, this pSLC mode is dynamic and variable in size. DapuStor’s implementation uses a fixed region sized by the operator, and the regions are exposed as individual block devices to the host. The J5060 is higher capacity, ranging from 15.36 to 122.88TB, utilizing the U.2 form factor for PCIe 4.0 x4. Endurance is rated at 0.5 Drive Writes Per Day over five years. The stock 30.72TB model is rated at 30,000 random-write IOPS at 16KB, with a write latency of 35 microseconds.
The capacity trade-off improves random writes by more than seven times, DapuStor stated. Average 4K random-write latency is reported below 8 microseconds. The pSLC features over 25 times the program/erase cycles of the QLC region. DapuStor achieves this through die-level isolation, optimized SLC reserve allocation, and region-aware I/O scheduling. The high-performance region targets workloads such as database journals, write-ahead logs, and metadata caches.
Industry Context and Alternatives
The NVMe specification has defined this arrangement since 2019 to enable one SKU to be configured by customers for specific use cases. A prior drive using a similar concept was the consumer Enmotus/Phison FuzeDrive P200. The distinct difference with DapuStor's approach is that it hands the host a second and separate block device with storage software control.
Competitors offer alternative solutions. Sandisk utilizes Direct Write QLC on its UltraQLC platform, which eliminates SLC buffering by enabling power-loss safe writes on the first pass. Alternatively, Micron offers a separate cache drive in its XTR, using 176-layer TLC entirely in SLC mode to act as an optional write buffer.
Questions remain regarding DapuStor’s drive, as specific pSLC region specifications are currently lacking. It remains uncertain what commands the drive employs and whether the region split is modifiable live. Balancing multi-bit flash in a single-bit mode for performance against the increasing need for capacity continues to present an industry-wide engineering challenge.
