The first generation used the V300 Toshiba 19nm Toggle-Mode 2.0 NAND Kingston but was replaced by Micron 20nm asynchronous NAND without notifying. The difference between the two is huge !! The Toshiba NAND has a maximum speed of 200 MB / s, while it is only 50 MB / s for the Micron NAND. Read more on anandtech.com/show/7763/an-update-to-kingston-ssdnow-v300-a-switch-to-slower-micron-nand amazon.com/Kingston-Digital-Adapter-SV300S37A-240G/product-reviews/B00A1ZTZNM The product with the 505/520 firmware is OK. But if you have the product with the 506/521 firmware, request a return.