Chapter 1. Kernel

The kernel in Red Hat Enterprise Linux 6.6 has been enhanced to enable user space to respond to certain SCSI Unit Attention conditions received from SCSI devices via the udev event mechanism. The supported Unit Attention conditions are:

Because SCSI Unit Attention conditions are only reported in response to a SCSI command, no conditions are reported if no commands are actively being sent to the SCSI device.

Red Hat Enterprise Linux 6.6 does not provide any default udev rules for these events, but user-supplied udev rules can be written to handle them. For example, the following rule causes a SCSI device to be rescanned if the inquiry data changes:

ACTION=="change", SUBSYSTEM=="scsi", ENV{SDEV_UA}=="INQUIRY_DATA_HAS_CHANGED", TEST=="rescan", ATTR{rescan}="x"

The rules for the supported events should match on the following SDEV_UA environment strings:

ENV{SDEV_UA}=="INQUIRY_DATA_HAS_CHANGED"
ENV{SDEV_UA}=="CAPACITY_DATA_HAS_CHANGED"
ENV{SDEV_UA}=="THIN_PROVISIONING_SOFT_THRESHOLD_REACHED"
ENV{SDEV_UA}=="MODE_PARAMETERS_CHANGED"
ENV{SDEV_UA}=="REPORTED_LUNS_DATA_HAS_CHANGED"

Note that in all cases the DEVPATH environment variable in the udev rule is the path of the device that reported the Unit Attention. Also, multipath I/O currently verifies that multiple paths to a device have some of the same attributes, such as the capacity. As a consequence, automatically rescanning a device in response to a capacity change can cause that some paths to a device have the old capacity and some paths have the new capacity. In such cases, multipath I/O stops using paths with the capacity change.

Red Hat Enterprise Linux 6.6 includes the Open vSwitch kernel module as an enabler for Red Hat's layered products. Open vSwitch is supported only in conjunction with products that contain the accompanying user-space utilities. Please note that without these required user-space utilities, Open vSwitch will not function and cannot be enabled for use. For more information, please refer to the following Knowledge Base article: https://access.redhat.com/knowledge/articles/270223.