scsa2usb - SCSI to USB bridge driver




The scsa2usb driver is a USBA (Solaris USB architecture) compliant nexus
driver that supports the USB Mass Storage Bulk Only Transport
Specification 1.0 and USB Control/Bulk/Interrupt (CBI) Transport
Specification 1.0. The scsa2usb driver also supports USB storage devices
that implement CBI Transport without the interrupt completion for status
(that is, Control/Bulk (CB) devices.) It supports bus-powered and self-
powered USB mass storage devices. This nexus driver is both a USB client
driver and a SCSA HBA driver. As such, the scsa2usb driver only supports
storage devices that utilize the above two transports.

The scsa2usb driver also supports a ugen(4D) interface allowing raw
access to the device, for example by libusb applications, bypassing the
child sd(4D) or st(4D) driver. Because a libusb application might change
the state of the device, you should not access the disk or tape

The scsa2usb nexus driver maps SCSA target driver requests to USBA client
driver requests.

The scsa2usb driver creates a child device info node for each logical
unit (LUN) on the mass storage device. The standard Solaris SCSI disk
driver or tape driver is attached to those nodes. Refer to sd(4D) or

This driver supports multiple LUN devices and creates a separate child
device info node for each LUN. All child LUN nodes attach to sd(4D) for
disks or st(4D) for tapes.

In previous releases, all USB disk storage devices were treated as
removable media devices and managed by rmformat(1) and volume management
software. In the current release, however, only disk storage devices
with a removable bit (RMB) value of 1 are removable. (The RMB is part of
the device's SCSI INQUIRY data.) See SCSI specifications T10/995D
Revision 11a, T10/1236-D Revision 20 or T10/1416-D Revision 23 for more
information. However, for backward compatibility, all USB disk storage
devices can still be managed by rmformat(1). With or without a volume
manager, you can mount, eject, hot remove and hot insert a 1394 mass
storage device as the following sections explain.

Some devices may be supported by the USB mass storage driver even though
they do not identify themselves as compliant with the USB mass storage

The scsa2usb.conf file contains an attribute-override-list that lists the
vendor ID, product ID, and revision for matching mass storage devices, as
well as fields for overriding the default device attributes. The entries
in this list are commented out by default and may be uncommented to
enable support of particular devices.

Follow the information given in the scsa2usb.conf file to see if a
particular device can be supported using the override information. For
example, by adding the following to the scsa2usb.conf file, many USB
memory sticks and card readers might operate more reliably:

attribute-override-list = "vid=* reduced-cmd-support=true";

Note that this override applies to all USB mass storage devices and might
be inappropriate for a USB CD writer. If so, you can add an entry for
each device to the attribute override list.

If USB mass storage support is considered a security risk, this driver
can be disabled in /etc/system as follows:

exclude: scsa2usb

Alternatively, you can disable automatic handling of a device as
described in the following subsection.

Using Volume Management

Disk storage devices are managed by Volume Manager. Software that manages
removable media creates a device nickname that can be listed with
eject(1) or rmmount(1). A device that is not mounted automatically can be
mounted using rmmount(1) under /rmdisk/label. Note that the mount(8) and
mount(8) commands do not accept nicknames; you must use explicit device
names with these commands.

See rmmount(1) to unmount the device and eject(1) to eject the media. If
the device is ejected while it is mounted, volume management software
unmounts the device before ejecting it. It also might kill any active
applications that are accessing the device.

Volume management software is hotplug-aware and normally mounts file
systems on USB mass storage devices if the file system is recognized.
Before hot removing the USB device, use eject(1) to unmount the file
system. After the device is removed, a console warning, such as "The
disconnected device was busy, please reconnect," might display. The
warning is harmless and you can ignore it.

You can disable the automatic mounting and unmounting of removable
devices by inserting a entry for a removable device in /etc/vfstab. In
this entry, you must set the mount at boot field to no. See vfstab(5).

Using mount and umount
Use mount(8) to explicitly mount the device and umount(8) to unmount the
device. Use eject(1) to eject the media. After you have explicitly
mounted a removable device, you cannot use a nickname as an argument to

Removing the disk device while it is being accessed or mounted fails with
a console warning. To hot remove the disk device from the system, unmount
the file system, then kill all applications accessing the device. Next,
hot remove the device. A storage device can be hot inserted at any time.


Disk block special file names are located in /dev/dsk, while raw file
names are located in /dev/rdsk. Tape raw file names are located in
/dev/rmt. Input/output requests to the devices must follow the same
restrictions as those for SCSI disks or tapes. Refer to sd(4D) or st(4D).


Refer to dkio(4I) and cdio(4I).


Refer to sd(4D) for disks or st(4D) for tapes.


The device special files for the USB mass storage device are created like
those for a SCSI disk or SCSI tape. Refer to sd(4D) or st(4D).


Block files for disks.


Raw files for disks.


ugen(4D) nodes


Raw files for tapes.


Symbolic link to the character device for the media in Zip drive 0


Symbolic link to the character device for the media in Jaz drive 0.


Symbolic link to the character device for the media in removable
drive 0. This is a generic removable media device.


64-bit x86 ELF kernel module


64-bit SPARC ELF kernel module


Can be used to override specific characteristics.


See attributes(7) for descriptions of the following attributes:

|Architecture | SPARC, x86, PCI-based systems |


cdrw(1), eject(1), rmformat(1), rmmount(1), ieee1394(4D), sd(4D), st(4D),
ugen(4D), usba(4D), pcfs(4FS), cdio(4I), dkio(4I), scsi(5), vfstab(5),
attributes(7), cfgadm_scsi(8), cfgadm_usb(8), fdisk(8), mount(8),

Writing Device Drivers

System Administration Guide, Volume I

Universal Serial Bus Specification 2.0

Universal Serial Bus Mass Storage Class Specification Overview 1.0

Universal Serial Bus Mass Storage Class Bulk-Only Transport Specification

Universal Serial Bus Mass Storage Class Control/Bulk/Interrupt (CBI)
Transport Specification 1.0

System Administration Guide: Basic Administration

SCSI Specification T10/995D Revision 11a -- March 1997

SCSI Specification T10/1236-D Revision 20 -- July 2001

SCSI Specification T10/1416-D Revision 23 -- May 2005


Refer to sd(4D) and st(4D).

In addition to being logged, the following messages may appear on the
system console. All messages are formatted in the following manner:

Warning: <device path> (scsa2usb<instance number>): Error Message...

Cannot access <device>. Please reconnect.

There was an error in accessing the mass-storage device during
reconnect. Please reconnect the device.

Device is not identical to the previous one on this port. Please
disconnect and reconnect.

Another USB device has been inserted on a port that was connected to
a mass-storage device. Please disconnect the USB device and reconnect
the mass-storage device back into that port.

Reinserted device is accessible again.

The mass-storage device that was hot-removed from its USB slot has
been re-inserted to the same slot and is available for access.

Please disconnect and reconnect this device.

A hotplug of the device is needed before it can be restored.

The following messages may be logged into the system log. They are
formatted in the following manner:

<device path><scsa2usb<instance number>): message...

Invalid <record> in scsa2usb.conf file entry.

An unrecognized record was specified in the scsa2usb.conf file.

Pkt submitted with 0 timeout which may cause indefinite hangs.

An application submitted a request but did not specify a timeout.

Syncing not supported.

Syncing after a panic is not supported. The filesystem may be

scsa2usb.conf override: <record>.

An override record specified in scsa2usb.conf was applied. Examples
of an override record applied to a device with vendor ID 123 and
product ID 456 are:

vid=0x123 pid=0x456 reduced-cmd-support=true


vid=* reduced-cmd-support=true

...meaning that the override record is applied to this device and all
other USB mass storage devices.


The Zip 100 drive does not comply with Universal Serial Bus Specification
1.0 and cannot be power managed. Power Management support for Zip 100 has
been disabled.

If the system panics while a UFS file system is mounted on the mass
storage media, no syncing will take place for the disk mass-storage
device. (Syncing is not supported by the scsa2usb driver.) As a result,
the file system on the media will not be consistent on reboot.

If a PCFS file system is mounted, no syncing is needed and the filesystem
will be consistent on reboot.

If a mass-storage device is busy, system suspend cannot proceed and the
system will immediately resume again.

Attempts to remove a mass-storage device from the system will fail. The
failure will be logged to the console. An attempt to replace the removed
device with some other USB device will also fail. To successfully remove
a USB mass-storage device you must "close" all references to it.

Concurrent I/O to devices with multiple LUNs on the same device is not

Some USB CD-RW devices may perform inadequately at their advertised
speeds. To compensate, use USB CD-RW devices at lower speeds (2X versus
4X). See cdrw(1) for details.

This driver also supports CBI devices that do not use USB interrupt pipe
for status completion.

May 23, 2021 SCSA2USB(4D)