Value-centric large capacity SSDs are on the horizon. OCZ Storage Solutions is in a good position to turn the SSD market on its head as parent company Toshiba finalizes SSD grade TLC NAND flash. Samsung started shipping 3 bit-per-cell NAND (TLC) in the original 840 SSD in October 2012, but the fast track cost the company, which led to higher retail SSD prices than what many expected. Toshiba and Micron spent more time developing TLC and timed production to coincide with advanced ECC technology that ensures mainstream endurance specifications.
Toshiba's Flash Forward NAND manufacturing partner, SanDisk, launched the TLC-based Ultra II SSD last September, but with pricing on par with MLC, the drive brings little value to the market. OCZ has a long history of delivering products at exceptional prices, even before the Toshiba acquisition. With guaranteed access to NAND flash and early priority, we expect OCZ to set the standard for low cost, high capacity SSDs.
There are still two hurdles for SSD manufacturers to overcome with TLC-based SSDs. The first is low sequential write performance once outside of the pSLC cache. The benchmark above is from a future competing product that shows the significant performance drop once the SLC cache layer is full. At that point, all of the data must write at TLC speeds.
We spoke with several companies about the ability to mask native TLC speeds and feel a dynamic cache is the best solution. As users add data to the drive, the pSLC layer will need to shrink, but most large sequential writes come early in the drive's lifespan as users populate the drive with applications and data. Over time, large sequential writes are few and far between, a movie here, a few music files there, but most of us don't move very large files after the initial installation. If SSD makers can hide native TLC performance long enough to get over the initial system setup process for users, then no one will care about lower out-of-burst performance.
The second issue with TLC right now is the program erase cycles. Our sources tell us that Toshiba SSD-grade TLC currently delivers 700 to 1000 P/E cycles before advanced ECC technologies built into the controller extend endurance to higher levels. OCZ's Trion 100 uses Toshiba's proprietary QSBC (Quadruple Swing-By Code) that dramatically improves the correction capabilities compared to LDPC used by other controller makers in upcoming products.
OCZ also has the advantage of working with Toshiba directly to gain deeper insight into the NAND flash. One theme we heard over and over at Computex is that the ability to bin flash from wafers is vital to success with future SSD products. TLC flash comes with a very wide grade scale; some flash is only useful in very low write environments. The percentage of TLC per wafer that can be used in an SSD is actually very low at this time.