[HN Gopher] USB Mass Storage and USB-Attached SCSI Are Both SCSI
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USB Mass Storage and USB-Attached SCSI Are Both SCSI
Author : hlandau
Score : 42 points
Date : 2020-09-11 11:07 UTC (11 hours ago)
(HTM) web link (www.devever.net)
(TXT) w3m dump (www.devever.net)
| xenadu02 wrote:
| SCSI rules the world I guess.
|
| ATAPI tunneled SCSI commands over PATA for CD drives and other
| such things.
|
| AFAIK SATA uses the SCSI command set too (as does Serial Attached
| SCSI obviously). To the point that most SAS controllers can also
| run SATA drives without issue.
|
| Apparently USB mass storage also uses SCSI in both BOT and UAS
| forms.
|
| Sometimes a protocol is designed so well to fit its purpose yet
| just flexible enough to support future use cases that there is no
| need to replace it. Hats off to the original designers of the
| SCSI command set.
| hlandau wrote:
| SATA doesn't use the SCSI command set. It's all still ATA,
| right down to the inability to abort tasks. (But it is common
| for operating systems, such as FreeBSD, to model all commands
| internally as SCSI commands and just translate them to ATA
| commands if necessary at the last minute.)
|
| SAS HBAs are backwards compatible with SATA drives because
| they're specifically designed to be. So I guess they're capable
| of passing either SCSI or, when SATA drives are used, ATA
| commands.
|
| Where it gets amusing is when you use SAS expanders, since then
| the link from the HBA to the expander is SAS, but the link from
| the expander to the drive is SATA. Thus SAS has a special
| protocol called Serial ATA Tunneling Protocol (STP), which
| allows ATA to be tunneled over SAS.
|
| What's really comical is that this means if you attached a SATA
| optical drive to a SAS expander, it follows that you'd be
| talking SCSI tunneled inside ATA/ATAPI tunneled inside STP over
| SAS.
| userbinator wrote:
| AFAIK the SATA just takes the set of registers an IDE drive
| would have, and puts them in a different physical/transport
| protocol.
| tlack wrote:
| Some protocols have so much persistence, where others seem to
| be tied to one vendor's fate.
|
| I wonder if its worth spending some time trying to understand
| what makes some protocols so robust and widely adopted. It's
| not just being open vs closed.
|
| A few other examples: - PostScript (probably) /
| PDF (iffy) - CAN (adaptable) - G-code -
| Serial - HTTP - HTML (sort of, badly) - VNC
| (maybe) - JSON (for now)
| msla wrote:
| Hayes command set, as expanded from land-line modems to GSM
| cell phones:
|
| https://en.wikipedia.org/wiki/Hayes_command_set
| tjr wrote:
| Years ago, I think when I was still using a Commodore Amiga
| system, I went into a computer shop in St. Louis to see if they
| had any SCSI drives.
|
| The clerk at the store went off on this surprisingly lengthy and
| heated diatribe about how SCSI was mediocre technology, and how
| nobody in their right mind should ever want anything SCSI ever
| again.
|
| I kind of miss that sort of passion in computer store clerks.
| hammock wrote:
| "Years ago" I was always told by my computer geekier friends
| that SCSI was better than IDE. And that you could put it in
| RAID arrays etc..
| bsder wrote:
| > The clerk at the store went off on this surprisingly lengthy
| and heated diatribe about how SCSI was mediocre technology, and
| how nobody in their right mind should ever want anything SCSI
| ever again.
|
| vs What in 1990? Pray tell. Parallel IDE? I'd have laughed in
| his face if he said that.
|
| The biggest problem with SCSI was always the fact that you had
| to understand _termination_ or the bus you built wasn 't going
| to work.
|
| The second biggest problem with SCSI was always the fact that
| it was more expensive. Cables were especially expensive, but
| controllers weren't cheap either.
| kevin_thibedeau wrote:
| Looks down at Ryzen PC with three SCSI CD-ROMs:
|
| "Hear that fellas? You're just mediocre."
| yjftsjthsd-h wrote:
| > Ryzen PC with three SCSI CD-ROMs
|
| Out of curiosity, what's that for? I'm struggling to think of
| a case where reading that many optical discs is actually
| useful
| reaperducer wrote:
| Can't speak for the OP, but I used a rig with three CDROMS
| on it to rip my wife's CD collection to the first iPod.
|
| It took months, but would have taken months longer if I
| only had one drive.
| jeffbee wrote:
| Sounds like a hassle. Didn't you need to buy a PCIe-SCSI HBA
| somewhere along the line, along with some kind of terminator
| for the upper half of a modern SCSI bus? Aren't very good
| SATA optical drives $20?
| kevin_thibedeau wrote:
| Some B350 boards still had legacy PCI slots. I have another
| PCI card I need to use so there was a spare slot left over.
| My use case was ripping CDs and for that you are better off
| using a longer wavelength CD-ROM laser and Plextor drives
| in particular for their better firmware capabilities.
| jmalicki wrote:
| ATAPI and SATA are also SCSI at their core.
|
| https://en.wikipedia.org/wiki/ATA_Packet_Interface
| hlandau wrote:
| You can tunnel SCSI over PATA/SATA using ATAPI, used for
| optical drives. That's a bit different from SATA being
| "SCSI at their core"; the entire point of ATAPI is that
| ATA isn't SCSI.
| UI_at_80x24 wrote:
| Passion related to computers as a hobby is the thing I miss.
| Once upon a time if your were "into computers" that meant
| something, now everybody thinks that they are into computers.
| "Like facebook right?" <eye-twitch>
|
| My first x86 PC had a 425MB SCSI-II hard-drive and a "triple
| Speed" (3x) CD-ROM. Having a SCSI drive with a seek time of
| UNDER 11ms was enough to blow the doors off of every other
| computer I came across (IIRC 4ms was the actual time vs 11ms
| for most other 120MB HD's at the time.)
|
| Everything about SCSI was cool. Over powered, over engineered,
| and willing to take abuse better then anything else.
|
| It was an AMD 386DX-40, 8MB of RAM, a VGA-Wonder XL video card,
| a Logitech bus mouse, soundblaster, and 2 modems; 14.4 & a 56k
| USR.
|
| AND I ran linux on it. Well I could install linux, and couldn't
| really figure out what to do with it after that. But Even back
| then Linux detected EVERYTHING, and it was FAST.
| geerlingguy wrote:
| The main thing I remember (I didn't worry as much about
| performance back then) was when I was grabbing a replacement
| from a pile of ribbon cables we had in a box, the wider ones
| were for SCSI, the narrower ones for IDE.
|
| Then SCSI-II and SCSI-III and ATAPI/UATA/PATA cables came
| along and started making the ease-of-identification based on
| just visual traits a lot more difficult.
| bonzini wrote:
| Why would anybody ever use ACA with either BOT (that doesn't
| support it) or UAS?
|
| It's basically a solution in search of a problem, since it is
| needed when commands are delivered asynchronously with respect to
| responses but you don't have autosense. BOT only has a single
| command in flight so it didn't need ACA, but UAS has autosense so
| it doesn't need it either...
| hlandau wrote:
| Author here. I'm no expert on the problems ACA was intended to
| solve, but if I understand it correctly, I could see some
| remaining applications for it.
|
| Suppose I schedule 10 commands all at once, with the Ordered
| task attribute. If the third command fails, do I necessarily
| want the remaining commands to be executed? Possibly these are
| a logical sequence (e.g. for a tape drive, rewind, write, etc.)
|
| I have no idea if anything actually exists which can make
| constructive use of ACA in this way, but it occurs to me that
| there is still potentially some use there even when autosense
| is enabled.
|
| That is, if I'm understanding ACA correctly.
| geerlingguy wrote:
| The article seems slightly pedantic in the argument that Mass
| Storage is "SCSI"--it implements a subset of the protocol, so
| yes, it has some bits of SCSI, but I don't think it follows to
| say "USB Mass Storage _is_ SCSI ".
| rektide wrote:
| I wonder what would change if we tried to nvme-ify.
|
| In the meantime I hope USB4 with pcie takes off. AMD needs to
| make it happen. Not enough mobile chip makers about for them to
| try to be competitive & throw in support on cell phones, not till
| 2026l5 or so I'd guess, even though it's be so neat & thoroughly
| bridge the chasm between pc & mobile.
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