random/sequential writes and ssd prices
Back when SCSI interfaces could to 1MB/s, you could reformat a SCSI disk with a new sector size. Microsoft can only handle 512 bytes/sector, so over time support for larger sectors disappeared. (Larger sectors mean a higher capacity because there are fewer inter-sector gaps, but waste time or space when many files are smaller than a sector.)
Nand flash typically has pages from 2 to 8K. Last time I used Nor flash, the page size was 64K. You can change any single 1 to a 0 in Nor flash, but it takes time. It is more efficient to write as many bytes at once with the chip allows (32 on that 16MB chip with 64K pages). The only way to change a zero to a one is to change all the zeroes to ones in an entire page. It used to be possible to change a few zeroes to ones in Nand flash. Modern devices cannot do this. It is only possible to write or erase an entire page.
When Nand flash is packaged up to pretend to be a hard disk, the operating system will issue some 512-byte writes all over the place. The wrong thing for the disk emulation layer to do is to read an entire 8K page, change 512 bytes of it, erase the page and write the data back. Sandisk have finally caught up with JFFS2.
JFFS2 is a Linux file system designed for Nor flash that is not hidden behind a hardware disk emulation layer. All writes are go sequentially to a single page until it is full, then the next erased page is used. This make some of the data on previous pages irrelevant when a more modern version is written. When there is only one erased page left, (or if there is a lull in disk activity), a full page is selected and its useful data is copied to the erased page and the selected page is erased. This leaves one erased page and one partially written page, so further writes can go into that partially written page.
JFFS2 is old tech. It takes a long time to mount large filesystems because the kernel has to read the entire device to map out where the most modern version of all the data is. OK for my ancient 16MB chip, but not so good for 1GB - which is a bit small by modern standards. There are newer shiner flash filesystems in Linux. Unfortunately I rarely get to play with them because most flash is hidden behind a defective disk emulator.
Nand flash comes in two flavours: ordinary, which is fast and costly per gigabyte and multilevel cell which is slow and cheap. You can make a fast SSD out of ordinary Nand flash, or by writing to multiple channels of multi-level flash simultaneously. The most profitable solution is to use multi-level flash with a single channel controller and sell it at a high price to people who do not check if the sustained transfer rate is tolerable.
Big SSD's are expensive because people will pay lots of money for the reduced latency. If you want these things at a good price, wait a bit.