> Furthermore if you are going to overwrite something in flash it usually behooves you to overwrite an entire block at a time. Well, all block devices are writ

> Furthermore if you are going to overwrite something in flash it usually behooves you to overwrite an entire block at a time. Well, all block devices are written a block at a time. The way flash differs is that there are two internal block sizes -- called pages (4-8kB), and eraseblocks (256kB-4MB). There are two states a page can be in: clear, or used. You can write at a page granularity, but only to clear pages. To clear used pages, you need to clear the entire eraseblock at a time. Eraseblock sizes are now limited by fundamental physical limits -- on every NAND node shrink from now, the eraseblocks are going to double in size. And they are already really huge in modern devices.