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I think this kind of design would have crap performance (or at least enforce it). The reason is that the disk controller has its own set of RAM that it employs

I think this kind of design would have crap performance (or at least enforce it). The reason is that the disk controller has its own set of RAM that it employs on the other end of the PCIe bus which could be battery backed and be designed to keep the controller alive long enough to flush everything. That’s not possible if the OS is in charge (the power requirements for the full OS are orders of magnitude higher). Additionally, you can’t have hybrid NVMe spinning rust disks with that kind of design. Finally, it’s unlikely that implementing it in the OS would be faster because there’s a bunch of flash translation logic and garbage collection that has to happen - much faster if all of that happens on the other side of the PCIe bus with a dedicated coprocessor with a dedicated SPI directly to raw flash.

josephg 3y ago
I’m imagining a software solution using some form of journaling / checkpoints. Instead of overwriting data in-place, send all writes to fresh, unused storage and then “commit” by updating a pointer to avoid write amplification. You’d need a bit of extra machinery to handle reads on the old data. As I understand it, NVMe drives already send all writes to unused space and then update pointers to reclaim old capacity. We could start with a nice implementation in the OS. Probably with a way for applications to opt in and out. And then optimize over time. Optimizations could include better integration with the way NVMe devices actually work, rather than the way they pretend to work to the rest of your computer.
- cobalt 3y ago
  file systems already do journaling and a bunch of other fancy techniques. Drives themselves then have their own versions in addition to that Additionally, apps can do whatever they want in custom partitions if they need better storage perf (databases for example do this). Getting lower level than that is probably doable, but you run the risk of becoming firmware that is tied to particular drive controller design Remember that computer storage technology is over 70 years old, many many things have been tried/implemented in that time.
  - josephg 3y ago
    File systems only do journaling for their own metadata. Has this been tried? It seems like an obvious idea to me, but operating systems have evolved remarkably little in the last few decades. Especially the filesystem.
    - cobalt 3y ago
      https://en.wikipedia.org/wiki/USN_Journal https://en.wikipedia.org/wiki/USN_Journal

josephg 3y ago

I’m imagining a software solution using some form of journaling / checkpoints. Instead of overwriting data in-place, send all writes to fresh, unused storage and then “commit” by updating a pointer to avoid write amplification. You’d need a bit of extra machinery to handle reads on the old data. As I understand it, NVMe drives already send all writes to unused space and then update pointers to reclaim old capacity. We could start with a nice implementation in the OS. Probably with a way for applications to opt in and out. And then optimize over time. Optimizations could include better integration with the way NVMe devices actually work, rather than the way they pretend to work to the rest of your computer.

cobalt 3y ago
file systems already do journaling and a bunch of other fancy techniques. Drives themselves then have their own versions in addition to that Additionally, apps can do whatever they want in custom partitions if they need better storage perf (databases for example do this). Getting lower level than that is probably doable, but you run the risk of becoming firmware that is tied to particular drive controller design Remember that computer storage technology is over 70 years old, many many things have been tried/implemented in that time.
- josephg 3y ago
  File systems only do journaling for their own metadata. Has this been tried? It seems like an obvious idea to me, but operating systems have evolved remarkably little in the last few decades. Especially the filesystem.
  - cobalt 3y ago
    https://en.wikipedia.org/wiki/USN_Journal https://en.wikipedia.org/wiki/USN_Journal