Comment by floatboth | Hacker News Reader

Comment by floatboth | Hacker News Reader

> Without UASP, a drive is mounted as a Mass Storage Device using Bulk Only Transport (or BOT), a protocol that was designed for transferring files way back in the USB 'Full speed' days

Wow, holy shit, TIL.. I was always assuming that USB drives were always SCSI — they show up as 'da' (Direct Attach) on FreeBSD after all.

Looking at umass driver source:

* The driver handles 3 Wire Protocols

* - Command/Bulk/Interrupt (CBI)

* - Command/Bulk/Interrupt with Command Completion Interrupt (CBI with CCI)

* - Mass Storage Bulk-Only (BBB) (BBB refers Bulk/Bulk/Bulk for Command/Data/Status phases)

* Over these wire protocols it handles the following command protocols

* - SCSI

* - UFI (floppy command set)

* - 8070i (ATAPI)

* UFI and 8070i (ATAPI) are transformed versions of the SCSI command set.

Huh, they are pretty much always SCSI, and "bulk only" is (unsurprisingly) only a USB transport level thing that doesn't change the command set.

I guess "UASP" is some sort of marketing term for Command/Bulk/Interrupt then..?

FreeBSD doesn't support UASP (protocol id 98). AFAIK neither do the other three BSDs.

Kudos for remembering DragonFlyBSD. We’re flattered.

Apparently as of 30 minutes ago FreeBSD does support it on the Pi 4! https://twitter.com/FreeBSDHelp/status/1280062935327313920

This is the PCI express driver for BCM2711. Good to see this but the UAS support would be elsewhere! Either in the umass driver or a new uas driver (just a guess as I am unfamiliar with the USB related kernel code).

Gah, you're right. Totally misread that tweet in my state of non-caffeinated stupor this morning. Still a useful improvement!

It isn't just a matter of speed. There are some drive commands that only work when you attach a device via an adapter that supports UASP. OPAL drive encryption being one.

Goals section:

https://en.wikipedia.org/wiki/USB_Attached_SCSI

> The native Intel USB3 UASP solution is only supported under Windows 8. To further complicate matters, not all Z77 motherboards support USB3 UASP. A license is required to implement UASP, and not all motherboard manufacturers are prepared to pass on the extra cost of this license to the end user

Sounds very cursed. I mean, I'm not a hardware vendor, I should not care, but licensing for something that's just another form of SCSI over USB sounds ridiculous.

I didn't know they even supported scsi, I knew about the old BOT-protocol and the huge limitations for harddrives over USB, and for that reason I've always avoided them whenever possible with the assumption that the basic limitations of the protocol was still true for 3.0 drives.

This does put USB-drive in a better light for me. I might event buy UASP supported USB 3.1g2/3.2 SATA-controller and do some testing myself.

I usually try to reach for a bus-connected controller which usually mean thunderbolt today for external enclosures (expensive), but it would be nice to build a portable DAS-array that can be connected to any device with USB-C.

As I understand it, it is a better USB layer/feature set to run SCSI on top of which has better properties. TFA gets into it a bit.

I think UASP adds command queuing and reduces some software overhead.

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