[wtallis]

There is some work on Open-Channel SSDs, that move most of the flash translation layer (FTL) to the host system. There are two major problems with this approach:

1. Each OS that wants to use the drive needs a compatible implementation of the FTL. Consumer systems always have at least two operating systems in play (UEFI counts for these purposes). Enterprise systems are where you will actually find non-boot data-only drives.

2. Flash memory changes. The FTL needs very different parameters depending on whether you're using Toshiba flash or Samsung flash, and even depending on whether you're using last year's Toshiba flash or the stuff they're manufacturing today.

These aren't insurmountable problems, but they're enough to keep such products confined to a small niche. Instead, we're seeing a trend of SSDs accepting optional hints that allow them to perform the kinds of optimizations you'd expect from a fully host-managed SSD. The ATA TRIM command was just the tip of this iceberg.

[_urga]

Could you provide more details on these hints? Are they ioctl calls? Assuming one is using the disk as a raw block device, without a filesystem.

[wtallis]

I was referring to extensions to the command set the OS uses to interact with the drive itself. Some of these are quite like a madvise() call, but at a lower layer. Others permit the drive to expose a bit more information to the OS so that it can better optimize its IO patterns. I summarized the most recently standardized changes at [1], but there are several other features in the NVMe spec [2] that fall into this category. The extension for IO determinism has been approved for the next standard but the official spec for it hasn't been published. (I'm referring here mostly to NVMe stuff, but there are SCSI/SAS analogs to many of these features.)

[1] https://www.anandtech.com/show/11436/nvme-13-specification-p...

[2] http://www.nvmexpress.org/resources/specifications/