For one of the SSDs, the first signs of weakness appeared when we polled the field after 100TB of writes. The SMART attributes of our Samsung 840 Series 250GB SSD revealed 11 reallocated sectors?bad blocks, in other words. Since the 840 Series' three-bit TLC NAND has lower write endurance than the two-bit MLC flash typically found in consumer-grade SSDs, we weren't surprised that it was the first to exhibit failures. All of our other candidates use MLC flash.
Despite those first bad blocks, the 840 Series' performance and user-accessible capacity remained unchanged. The same was true for the other SSDs, so we set our sights on 200TB.
At the latest milestone, the 840 Series is up to 370 reallocated sectors. It's not the only one with bad blocks, either. One of our Kingston HyperX 3K 240GB drives?the one we're testing with incompressible data like the other SSDs?reports four bad blocks. We also have an identical HyperX drive that's being tested with 46% compressible data, but it remains free of flash failures. That drive has only written 143TB to the flash thanks to its SandForce-powered compression tech, so we're not surprised that it's in better shape than its twin.
