SanDisk 240 GB Extreme II SSD Review

SanDisk releases its Extreme II series SSD, which features the Marvell 9187 controller in concert with 19nm eX2 ABL MLC NAND. The competition is heating up as another manufacturer with massive foundry capabilities releases a new SSD. Will the Extreme II "blaze through your day" and "keep you ahead of deadlines?"



The SanDisk Extreme II features 550/510 MB/s in sequential read/write speed, and 95,000/78,000 random read/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 eight channel Marvell 9178 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 be exhausted long before this point.

The SSD also features various capacities of SanDisk DRAM for caching purposes. The DDR3-1600 DRAM scales with capacity, the 120GB, 240GB and 480GB SSDs feature 128MB, 256MB, and 512MB of DRAM, respectively. The DRAM cache is part of a tiered caching approach from SanDisk that is designed to minimize wear and enhance performance.

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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.

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SanDisk also provides its "SSD Toolkit." This utility provides information on the SSD, such as the firmware revision and SMART data attributes. SMART data can be used to monitor the health and expected lifetime of the SSD. The utility also provides a much-needed easy method for updating firmware. Many SSDs require the user to jump through hoops to find and download firmware.

Many times this can also involve complicated steps, such as creating bootable media such as a CD or USB stick, to perform the update. This can be very frustrating because this also requires the user to learn how to create that bootable media. One of the keys to gaining mainstream adoption for SSDs is to make this process end-user friendly.

SanDisk has succeeded in this respect with its SSD Toolkit. This utility will check for a firmware update and then download the firmware if prompted to do so. The user is then prompted to insert either a blank CD or USB stick, and the utility will not only insert the firmware update to the chosen medium but also make it bootable. This streamlines the process tremendously and is one feature that we would like to see other manufacturers include as a standard.

Availability and Warranty


The SanDisk Extreme II comes in capacities of 120GB, 240GB, and 480GB. The SSDs carry a five-year warranty.

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