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Comment by zokier | Hacker News Reader

Right now it is not even clear how to interface with SSDs even on a single host, there has been all sorts of attempts to move away from the traditional plain block device model. NVMe has extensions for KV, ZNS, and FDP, all which offer different characteristics. And then there are of course open channel SSDs and some others too. I kinda expect the future foundational IO interface to be more S3-like than block-device or unixy filesystem-like.

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I really wish reviewers would harp on FDP (Flexible Data Placement) and perhaps KV support. FDP supposedly somewhat ate ZNS as a spec, allegedly, but there might be gaps, reasons to keep ZNS.

There's only a small little mention, if we are lucky, on the couple drives that have it (expensive enterprise flagships). It should be a regular sticking point, whether it's there or not. Without pressure it's not going to get regularly available, it feels like.

FDP is so simple. Declare a number for what pool of data you want to write into. Data of the same pool gets written to the same storage such that you can wipe it latter together. It has huge wins though against write amplification! Massive wins. For so close to free.

Some day I want to own a FDP drive. And then I can finally start using the tokio/io-uring support that I contributed! https://github.com/tokio-rs/io-uring/issues/380

The NVMe-KV is more radical. Still worth putting some pressure on, but your drive as KV, as object store, feels harder. Side note, really enjoyed this ceph nvme-kv offload post thing, my favorite tech write up in a while! https://ceph.io/en/news/blog/2026/for-whom-the-door-bell-tol...

FDP relies on putting logic on the drive side, then they can upcharge for drives with this feature and still give you limited control. If you go the other direction instead, you have MTD devices which gives the host system kernel full control over data placement, page erasing and error correction, and for this reason they need specialized filesystems. These devices usually aren't attached over PCIe as they use controllerless raw flash interfaces instead, but in principle they could be.

I'm very much a fan of open channel flash. My understanding is that the Open Channel flash people when they tried a decade ago basically got told no by drive makers, that the drive makers weren't interested in becoming commodity vendors, and were intent on keeping product lines somewhat as they were. I wish I had some links to share to back this up, but that's basically my recall. ZNS and then FDP was sort of a compromise to give people some of the wins they were looking for, while basically not disrupting the product.

FDP is a very minimal addition of control. But yes it is another box to ticket, is another place to upcharge. Yet still, we're only just seeing mainstream products emerge. Kioxia's CM10 for example. https://www.techpowerup.com/351218/kioxia-introduces-first-p...

I'm hoping that the need is great enough to break the industry control. I think for a while the market felt relatively well enough served such that it was unclear whether clear wins would actually result in customers. With AI need for speed, I can definitely imagine incredibly crazy CXL controllers or what not, that allow low latency acces to many many open channel flash systems. Wouldn't that be a thing.

Again though, FDP is such a ridiculously tiny add, and it helps SSDs so much for so many use cases. I really hope it becomes an expectation, not a feature, sooner rather than latter.

Edit: happy to see a new group has shown up asking for open channel flash, Open Flash Platform. https://openflashplatform.org/

Why would it be S3-like? S3 is a very general abstraction on storage. If there's room below the current abstractions, it's below, not above - Linux has drivers for raw flash devices (mtd devices) which gives Linux full control of the program/erase cycle and responsibility for wear-leveling.

I would assume “S3-like” in the sense that objects are immutable, large writes, separate metadata storage, etc. Patterns that fit modern SSDs better than the abstractions of block devices.

Yea, exactly, I was thinking the direction of for example how Ceph Seastore and WDs ZenFS bypass the traditional block device and vfs layers and do their own thing, combined with what nvme has been doing with these new extensions (kv, zns, fdp). Not really sure if "more s3-like" is completely accurate description of that direction, but to me it seems somewhat reasonable reference.

They don't really though. You can incrementally write an SSD. What you're proposing might be a useful abstraction for some applications but it's not closer to the metal, and it fits an HDD (especially SMR) or a tape even better than it fits an SSD.

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