USB devices and smartmontools

To access USB storage devices, the operating system sends SCSI commands through the USB transport to the device. If the USB device is actually a PATA or SATA disk in an USB enclosure, the firmware of its USB bridge chip translates these commands into the corresponding ATA commands. This works straightforward for read and write commands, but not for SMART commands.

To access SMART functionality, smartmontools must be able to send ATA commands directly to the disk. For USB devices, at least the following conditions must be met:

• The USB bridge provides an ATA pass-through command.
• This command is supported by smartmontools.
• The operating system provides a SCSI pass-through I/O-control which works through its USB-layer.
• SCSI support is implemented in the operating system interface of smartmontools.

Some recent USB bridges already support the vendor independent SAT (SCSI/ATA Translation, ANSI INCITS 431-2007) standard. Other USB bridges provide vendor specific ATA pass-through commands. The current version of smartmontools supports the following pass-through commands and USB bridges:

Command	USB bridges	smartctl option	48-bit ATA support	Comment
SAT ATA pass-through 12 and 16	various (Initio, Oxford, ...)	-d sat[,16]; -d sat,12	requires '-d sat[,16]'	Older Linux kernels may require '-d sat,12'
Cypress ATACB	Cypress CY7C68300B/C (AT2LP), CY7C68310 (ISD-300LP)	-d usbcypress[,CMD]	No	CY7C68300A (AT2) may not work.
JMicron ATA pass-through	JMicron JM20329, JM20335-39	-d usbjmicron[,x][,PORT]	No:JM20327, Yes:JM20336/9	'-d usbjmicron,x' enables 48-bit support
Sunplus ATA pass-through	Sunplus SPIF215/6, SPIF225/6	-d usbsunplus	Yes

Smartmontools was successfully tested with many USB devices on several Platforms. This will never work on MacOS X unless someone adds SCSI pass-through support to this OS. If the USB ID can be obtained from the operating system, smartmontools also supports auto-detection of (the already tested) USB devices. Then it is not necessary to specify the '-d' option. See the following table for details:

Platform	...has SCSI pass-through	smartmontools supports SCSI	... supports USB	... auto-detection	... in smartd DEVICESCAN	Comment
Linux	Yes	Yes	YES	YES	YES	See comment about SAT in above table
MacOS X	No	No	No	No	No	USB works with e.g. XP in a VM
FreeBSD	Yes	Yes	YES	YES	YES
NetBSD	Yes	Yes	YES	No	No
OpenBSD	Yes	Yes	YES	No	No
Solaris	Yes	Yes	YES	No	No
QNX	?	No	No	No	No
OS/2	?	No	No	No	No
Windows NT/2K/XP/Vista	Yes	Yes	YES	YES	No	Auto-detection is slow due to the use of 'wmic.exe'
Windows 9x/ME	Yes	Yes	YES	No	No	Requires ASPI driver