SanDisk Ultra Plus 256GB SSD Review
The SanDisk Ultra Plus features SanDisk's proprietary eX2 ABL MLC NAND with nCache technology. This technique creates a SLC layer to help boost write performance and enhance endurance. The SSD also features a four channel Marvel 88SS9175 controller and 128MB of DRAM cache.
The SanDisk Ultra Plus features 530 MB/s in sequential read and 445 MB/s of sequential write speed. For random performance the Ultra Plus provides 82,000 read IOPS and 39,000 write IOPS. The SSD comes in a standard 2.5 inch form factor with a 7mm Z-Height, which will enable its deployment into many current laptops.
The SSD uses the Marvell 9175 in conjunction with 19nm eX2 ABL MLC NAND and all capacities of the drive are rated for 80 TBW (TeraBytes Written). The SSD features a 2 million hour MTBF (Mean Time Between Failure) rating, though the NAND's endurance would surely be exhausted long before this point. The SSD also features 128MB of SanDisk DRAM for LBA mapping purposes.
The SSD includes a SSD Toolkit which can be download from SanDisks website. This toolkit provides users with firmware updates and SMART data for lifetime monitoring. This toolkit is helpful, but we would like to see secure erase support added to the package.
Typically SSD controllers utilize several approaches to limit the amount of wear on the NAND, and one of the most effective approaches is write combining. This essentially combines several small random writes into one large sequential write. Due to the nature of SSDs this creates less wear on the NAND, increasing the endurance of the SSD.
SanDisk has chosen to set aside a portion of the NAND to operate as a larger cache buffer, to intelligently cache small random write activity so that it can be aggregated and written down to the flash as large sequential writes. This process of write combining is standard fare, but SanDisk has chosen to utilize a layer of SLC NAND for caching. As we can observe in the diagram above SanDisk has programmed a section of each NAND die to operate as SLC NAND. This is accomplished by simply only storing one bit per cell in the MLC NAND.
The benefit of SLC is that it has 100,000 P/E Cycles (Program/Erase), compared to a mere 5,000 P/E Cycles for standard MLC. This massive increase in endurance for this 'layer' provides a great medium to use as a scratch area, pooling the small random writes until these are written down to the underlying MLC NAND. This approach should also provide a decrease in write latency.
Availability and Warranty
The SanDisk Ultra Plus is available in capacities of 64GB, 128GB and 256GB. There seems to be limited availability of the 64GB capacity Ultra Plus at this time, leading to a significantly higher than normal price point for that model.
The SSD only offers a three year warranty, which is comparatively low in relation to other MLC products.