Filesystem-level compression isn't magic, you still have to write data in sector-sized chunks to the underlying device. And while individual flash chips still u

Filesystem-level compression isn't magic, you still have to write data in sector-sized chunks to the underlying device. And while individual flash chips still use 512 byte sectors (pages), modern SSDs flash controllers gang them up in parallel, so the smallest "sector" you can write from the host side is still 4KB and up. Which means, when you're doing single-page writes on the host, compression doesn't save you anything at the device level. For large data items, you can obviously save space if the uncompressed size is larger than a couple of pages. But then you lose CPU time on the access. Typically, with very large data items, when you retrieve them, you may only need a couple small pieces, not the entire item. If you've compressed the entire value though, you must decompress the entire thing before you can use any of it. If you do piecewise page-level compression, then you're back to the problem of not saving any space unless you can guarantee better than 50% compression per page, to fit at least 2 compressed pages per physical page. And nobody gets better than 50% compression on arbitrary binary data without expending a lot of CPU cycles. To get really good compression ratios you need to be able to analyze a larger volume of data (and of course there has to be low enough entropy in the data itself). So if you're restricted to page-sized chunks to compress, you'll never get enough of a window to achieve great compression ratios. (PS: I've done plenty of work on data compression. https://en.wikipedia.org/wiki/ARC_%28file_format%29 https://en.wikipedia.org/wiki/ARC_%28file_format%29 )