Thumbstick vs HD

Peter Van Hove peter at Smart-Projects.net
Sun Sep 18 01:34:02 PDT 2011


Formatted message: <a href="http://www.t10.org/cgi-bin/ac.pl?t=r&f=r1109182_f.htm">HTML-formatted message</a>

Thanks John,
>  is to look for the protocol
I fear that is a bit too deep for my software to check I'm afraid.
Monday I'm going to look into bit 7 of byte 1 of the Inquiry command return
data and check that on the test devices I have here.
But if I understand you correctly, there may be jumpdrives that report 'not
removable' ?
I'm curious to test my USB hard drives, to see what they report here.
Peter
------------------------------------------------------------------
  ----- Original Message ----- 
  From: John Geldman (jgeldman) 
  To: Peter Van Hove ; T10 Reflector 
  Sent: Sunday, September 18, 2011 8:45 AM
  Subject: RE: Thumbstick vs HD
  I'm not sure what you want to distinguish between. 
  Are you looking for hints on removability?
  Are you looking for USB/SATA bridged SSD's or HDD's? 
  Or to distinguish USB jumpdrives designed for use as media/copy storage
devices? Unfortunately, a USB jumpdrive can be as boot-ready as a USB-SATA
bridged device.
  RMB:
  In the data returned by INQUIRY, there is an RMB bit (byte 1, bit 7) that
describes a controller that supports removable media. Think of a DVD drive
with a removable disk, or a USB card reader. In these removable media cases,
the controller is around to report whether or not the media is present. This
just doesn't apply to USB jumpdrives: when a USB device is yanked, the
controller leaves too.
  However, certain common OS's have used this reported bit to change the
caching and access strategy for USB storage devices. And sometimes said OS's
and their maintainers may be schizoid on what the policy changes. That may be
an opinion. Some OS's require the bit to cleared for the device to be
considered bootable.
  The bottom line for RMB is that  some USB devices set the RMB bit and some
don't. Most consumer devices have it set (removable media), but some
performance devices have it cleared (non-removable media). Some vendor's have
produced vendor specific tools to change the value of this bit.
  Protocol:
  Almost all USB 2.0 USB jumpdrives and most early USB 3.0 jumpdrives use the
USB protocol, Bulk-Only Transport (BOT). This is a single threaded flow, with
a USB packet wrapping the command block, a series of USB packets wrapping the
data block (in or out), followed by a USB packet wrapping the command status,
to be followed with yet another command sequence. 
  New USB 3.0 jumpdrives and potentially new USB 2.0 jumpdrives can use UAS.
UAS/UASP was defined partly in T10 and partly in USB-IF (USB Across SCSI as
defined in T10, and USB Across SCSI Protocol in USB-IF). This enables robust
full command queuing. Full command queuing is an essential ingredient to the
functionality we expect for boot storage performance.
  So, the bottom line for SSD-type performance (as opposed to media or copy
centric storage, which still has a place in the market) is to look for the
protocol. BTW, this applies to devices with native or bridged controllers.
  SAT:
  Finally, some USB/SATA devices that implement SAT (SCSI ATA Translation)
support a VPD page that provides ATA's IDENTIFY DEVICE data parameters. This
will  identify a bridged device.
  I hope I hit the main areas you were looking for.
  Regards,
  John Geldman
  Director, Industry Standards
  Lexar Media Inc. (a Micron Technology Inc. subsidiary) 
  47300 Bayside Parkway Fremont, CA 94538
  P: 510-580-8715
  C: 510-449-3597
  From: owner-t10 at t10.org [mailto:owner-t10 at t10.org] On Behalf Of Peter Van
Hove
  Sent: Saturday, September 17, 2011 9:00 AM
  To: T10 Reflector
  Subject: Thumbstick vs HD
  Hi,
  Is there a way (and if so, what is it) to distinguish between a (removable)
thumbstick (memory stick or card) and a (removable) HD ?
  I would like to recognize what is what.
  Peter



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