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What: /sys/class/scsi_host/hostX/isci_id
Date: June 2011
Contact: Dave Jiang <>
This file contains the enumerated host ID for the Intel
SCU controller. The Intel(R) C600 Series Chipset SATA/SAS
Storage Control Unit embeds up to two 4-port controllers in
a single PCI device. The controllers are enumerated in order
which usually means the lowest number scsi_host corresponds
with the first controller, but this association is not
guaranteed. The 'isci_id' attribute unambiguously identifies
the controller index: '0' for the first controller,
'1' for the second.
What: /sys/class/scsi_host/hostX/acciopath_status
Date: November 2013
Contact: Stephen M. Cameron <>
Description: This file contains the current status of the "SSD Smart Path"
feature of HP Smart Array RAID controllers using the hpsa
driver. SSD Smart Path, when enabled permits the driver to
send i/o requests directly to physical devices that are part
of a logical drive, bypassing the controllers firmware RAID
stack for a performance advantage when possible. A value of
'1' indicates the feature is enabled, and the controller may
use the direct i/o path to physical devices. A value of zero
means the feature is disabled and the controller may not use
the direct i/o path to physical devices. This setting is
controller wide, affecting all configured logical drives on the
controller. This file is readable and writable.
What: /sys/class/scsi_host/hostX/link_power_management_policy
Date: Oct, 2007
KernelVersion: v2.6.24
(RW) This parameter allows the user to read and set the link
(interface) power management.
There are four possible options:
min_power: Tell the controller to try to make the link use the
least possible power when possible. This may sacrifice some
performance due to increased latency when coming out of lower
power states.
max_performance: Generally, this means no power management.
Tell the controller to have performance be a priority over power
medium_power: Tell the controller to enter a lower power state
when possible, but do not enter the lowest power state, thus
improving latency over min_power setting.
med_power_with_dipm: Identical to the existing medium_power
setting except that it enables dipm (device initiated power
management) on top, which makes it match the Windows IRST (Intel
Rapid Storage Technology) driver settings. This setting is also
close to min_power, except that:
a) It does not use host-initiated slumber mode, but it does
allow device-initiated slumber
b) It does not enable low power device sleep mode (DevSlp).
What: /sys/class/scsi_host/hostX/em_message
What: /sys/class/scsi_host/hostX/em_message_type
Date: Jun, 2008
KernelVersion: v2.6.27
em_message: (RW) Enclosure management support. For the LED
protocol, writes and reads correspond to the LED message format
as defined in the AHCI spec.
The user must turn sw_activity (under `/sys/block/*/device/`)
OFF it they wish to control the activity LED via the em_message
em_message_type: (RO) Displays the current enclosure management
protocol that is being used by the driver (for eg. LED, SAF-TE,
SES-2, SGPIO etc).
What: /sys/class/scsi_host/hostX/ahci_port_cmd
What: /sys/class/scsi_host/hostX/ahci_host_caps
What: /sys/class/scsi_host/hostX/ahci_host_cap2
Date: Mar, 2010
KernelVersion: v2.6.35
[to be documented]
What: /sys/class/scsi_host/hostX/ahci_host_version
Date: Mar, 2010
KernelVersion: v2.6.35
(RO) Display the version of the AHCI spec implemented by the
What: /sys/class/scsi_host/hostX/em_buffer
Date: Apr, 2010
KernelVersion: v2.6.35
(RW) Allows access to AHCI EM (enclosure management) buffer
directly if the host supports EM.
For eg. the AHCI driver supports SGPIO EM messages but the
SATA/AHCI specs do not define the SGPIO message format of the EM
buffer. Different hardware(HW) vendors may have different
definitions. With the em_buffer attribute, this issue can be
solved by allowing HW vendors to provide userland drivers and
tools for their SGPIO initiators.
What: /sys/class/scsi_host/hostX/em_message_supported
Date: Oct, 2009
KernelVersion: v2.6.39
(RO) Displays supported enclosure management message types.