> then each write will consume less time for looking up if the specific sector is contained in the datastructure. For most SSDs, this lookup is a single DRAM

> then each write will consume less time for looking up if the specific sector is contained in the datastructure. For most SSDs, this lookup is a single DRAM fetch per 4kB of user data, and therefore much faster than even a single NAND flash read, let alone a NAND flash program or erase operation. The reason that imaging a SSD is faster after it's been trimmed or secure erased is that every erase block is empty and ready to accept new data. When you overwrite data on a used disk, the drive has to free up erase blocks and that generally involves moving old data elsewhere to preserve it—because the drive doesn't know that the commands to overwrite that are also coming soon.