Kioxia revisits SLC flash to power FL6 and rival Optane

Solid-state storage maker Kioxia has announced the FL6 BiCS4 XL-Flash, which uses single level cell (SLC) NAND flash to provide performance and endurance for applications such as storage-class memory and to rival Intel’s Optane product.

Kioxia’s FL6 BiCS4 XL-Flash provides a claimed read throughput of 6.2GBps and 5.8GBps on writes, with 1.5 million read IOPS and 0.4 million on writes. Latency is in the low tens of microseconds for reads and writes.

That’s close to Intel’s Optane P5800X, which reads data at 7.2GBps, with 1.5 million input/output operations per second (IOPS) and 6 microseconds of latency, and with write throughput of 6.5GBps.

Presumably, the Kioxia product aims at being competitive on cost. The company hasn’t revealed the cost of the FL6, but it would be safe to assume it will be cheaper – with its use of commodity flash storage – than Optane’s 3D Xpoint.

FL6 and Optane connect via PCIe 4.0 and run two channels. Intel plans to announce the P5801X, which will be a little quicker, with throughput of 7.4GBps for reads and writes.

Kioxia’s FL6 is based on its so-called XL-Flash, which is built on SLC NAND flash. SLC was the first generation of NAND flash to hit the market before being superseded for general storage use by MLC, TLC, QLC, and so on.

With only one charge per cell, SLC is the most rapid of the NAND flash generations and has the longest lifespan, but also offers the least in terms of capacity, with 96 layers of cells accessible via 16 parallel buses in the case of the FL6 chip.

Use of SLC limits capacity, but that’s not the key aim here – performance is the main requirement. FL6 products will be available initially in 800GB, 1.6TB and 3.2TB capacities, which are the same as those available in the P5800X family from Intel.

What SLC does offer to the FL6 is long endurance, with a guarantee of five years, which compares to around a year of life from ordinary QLC SSDs.

Also using SLC is the Samsung-developed Z-SSD, which is little-changed since its launch in 2019. With 48 layers of SLC, the Samsung SZ985 offers much lower performance than the Kioxia FL6, namely 3.4GBps throughput for reads and 3GBps for writes, with 0.75 million read IOPS and 0.17 million during writes.

Samsung’s Z-SSD connects via PCIe 3.0, which is 2x less speedy, and via four channels that allow for read latency of 20 microseconds in reads and 16 microseconds for writes.

A year ago, Kioxia launched an solid-state drive (SSD) with similar throughput, the CM6, which has 96 layers of TLC flash. Use of TLC flash limited endurance and its use in write-intensive environments, such as with databases, and left the field open to Optane.

According to analysts TrendForce, Kioxia ranks second among global SSD makers with 18.3% of the market, behind Samsung (34% market share). Kioxia, however, is a target for takeover by Western Digital (14.7% market share), which plans to invest $20bn in product development and to take the place of Samsung.

For its part, Intel (6.7% market share) is set to redouble its efforts on the Optane front, based on a shift to 3D Xpoint and away from NAND flash activity, which Intel sold to SK Hynix (12.3% market share).

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