Toshiba Takes On Optane With 3D XL-Flash: High Performance Meets Low Cost

Toshiba announced at the Flash Memory Summit that it's developing 3D XL-Flash, which is a high-performance variant of existing flash that purportedly provides a 10X reduction in read latency compared to the TLC flash found in most consumer SSDs. The move comes as a somewhat belated response to Intel's high-performance Optane products that are powered by the exotic, and expensive, 3D XPoint memory.

In theory, Toshiba's XL-Flash sounds very similar to Samsung's Z-NAND, which also competes with Intel's Optane. Both new types of NAND offer enough performance to come within striking range of Intel's Optane in the performance measurements that matter, but will come at a much lower price point because they use proven technologies that the companies already produce on a massive scale. Ultimately, that means the new type of flash can undercut Intel's Optane on price by a significant amount, but Toshiba hasn't shared specifics yet.

Speedy Optane memory has come to market as both storage and caching devices, but high prices have kept the devices, which are significantly faster than normal SSDs, from replacing flash-based SSDs. Currently, Optane retails for roughly $0.60 per GB, but normal flash-based SSDs can dip as low as $0.15 per GB. The 4X price premium might seem reasonable for a superior device, but latency introduced by the drive's controller and firmware, along with the interface and the file system, ultimately reduce much of Optane's performance advantage in real-world applications. That leaves an opening for devices that are cheap and "good enough."

Toshiba's new flash memory features shorter bitlines and wordlines, which are internal connections to the flash cells, to improve performance. The flash also has more planes, which are independent regions of the flash that can respond to data requests simultaneously, to improve parallelism, and thus performance. XL-Flash is based on Toshiba's tried-and-true BiCS flash, but Toshiba uses the existing flash in SLC mode, meaning it only stores one bit per cell to increase performance.

As a result, XL-Flash provides program times of a mere 7 microseconds, which is much faster than QLC's 30 microsecond program time. Of course, the increased performance comes at the expense of storage density, but Toshiba obviously feels the high performance will offset the die capacity reduction.

At first, Toshiba will use XL-Flash as SLC cache to complement its QLC flash, as a high-performance cache for the larger and cheaper QLC flash devices. Toshiba claims the pair can offer better overall latency than DRAM paired with an HDD storage pool. Much of this advantage is due to XL-Flash's capacity advantage over DRAM, which allows for more cache hits during real-world workloads.

Toshiba will start with SLC-based XL-Flash devices but is considering MLC variants of the high-performance flash as well. The initial products are destined for the data center, but like most high-performance tech, it should filter down to the desktop PC in due course.

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