With their advantages of higher access speeds, lower power consumption, small form factor size, and greater reliability, it comes as no surprise that SSDs are replacing HDDs in the marketplace. Plus, there’s the market trend of SSDs with higher capacities and lower cost per GB unit year by year.
Thanks to 3D NAND technology, which allows for the vertical stacking of memory cells, storage units can be stacked in multiple layers, increasing the size of each storage unit and the capacity in the NAND. Furthermore, TLC SSDs can be more reliable at a much friendlier price.
Since the market is chasing higher and higher SSD capacity, Phison, as the pioneer of SSD technology development, keeps pursuing innovative new technologies to optimize the usage of NAND flash to gain the highest user capacity in SSD products.
In the past, to ensure that each flash on an SSD module had enough good blocks to achieve full capacity, Phison used flash sorting in its mass production flow. Flash sorting, however, takes time and requires additional cost. Therefore, Phison developed a new methodology called Smart X Block to optimize a superblock’s composition and save time and cost during the sorting process.
Traditional super block management algorithm
Previously, the method used to compose a superblock was by taking one physical block from each plane.
All superblocks consist of one physical block from Plane0 to Plane15. Since Plane0 only has N+2 good blocks (which is the lowest good block number among all planes), this device, as limited by Plane0, can only make N+2 superblocks. Even if Plane1 to Plane15 still have lots of good blocks left, these blocks cannot make superblocks to increase the device’s capacity and are used only as spare blocks.
In other words, the minimum good block amount among all planes limits the overall superblock number (device capacity). If the minimum good block amount is less than the total capacity threshold, it means the device cannot create enough superblocks to achieve full capacity.
Phison used to sort flash with different grades according to its good block amount and would make full capacity SSDs with higher grades, such as Bin1, in which the good block amount was more than the full capacity threshold.
Over time, the bad blocks of each plane will gradually increase during SSD usage. Once any of the planes reached the write-protect threshold, this SSD would become write-protected.
In this example, Plane1 has reached its maximum bad block amount. Even though Plane0 and Plane2 to Plane15 still have lots of good blocks left, the device will enter write-protect mode, and all the good blocks left in other planes will not be able to be used anymore.
Traditional superblocks cause the waste of flash block usage, so Phison developed a new technology to overcome this issue.
Superblock management with Smart X Block technology
Smart X Block changes the way superblocks are composed. With this new firmware architecture, Phison doesn’t need to take physical blocks from each plane. Since their firmware can compose superblocks across different planes, the average number of good blocks from all planes determines the overall superblock number. In other words, with Smart X Block, the minimum good block amount across all device planes will not be the ceiling of the superblock number.
If the initial average good block number is higher than the full capacity threshold, this device has enough superblocks to achieve full capacity. The device will only not become write-protected with the new methodology if the average good block number remains less than the write-protect threshold.
Smart X Block extends an SSD’s lifetime and reduces block wastage because all the blocks in each plane achieve full utilization before write-protection is triggered.
Phison takes the lead once again
To keep the lead in the race to achieve higher SSD capacity, Phison developed the new Smart X Block technology to maximize flash usage and achieve the highest user capacity without implementing a flash sorting process. Smart X Block enables a more flexible way to compose superblocks that optimize the use of flash and increases SSD lifetime.
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