Installation guide

Chapter 21. Online Storage Management
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For more information about multipathing, refer to the Using Device-Mapper Multipath
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guide (in http://
www.redhat.com/docs/manuals/enterprise/).
21.15. Adding/Removing a Logical Unit Through rescan-
scsi-bus.sh
The sg3_utils package provides the rescan-scsi-bus.sh script, which can automatically
update the logical unit configuration of the host as needed (after a device has been added to the
system). The rescan-scsi-bus.sh script can also perform an issue_lip on supported devices.
For more information about how to use this script, refer to rescan-scsi-bus.sh --help.
To install the sg3_utils package, run yum install sg3_utils.
Known Issues With rescan-scsi-bus.sh
When using the rescan-scsi-bus.sh script, take note of the following known issues:
• In order for rescan-scsi-bus.sh to work properly, LUN0 must be the first mapped logical unit.
The rescan-scsi-bus.sh can only detect the first mapped logical unit if it is LUN0. The rescan-
scsi-bus.sh will not be able to scan any other logical unit unless it detects the first mapped
logical unit even if you use the --nooptscan option.
• A race condition requires that rescan-scsi-bus.sh be run twice if logical units are mapped for
the first time. During the first scan, rescan-scsi-bus.sh only adds LUN0; all other logical units
are added in the second scan.
• A bug in the rescan-scsi-bus.sh script incorrectly executes the functionality for recognizing a
change in logical unit size when the --remove option is used.
• The rescan-scsi-bus.sh script does not recognize ISCSI logical unit removals.
21.16. Modifying Link Loss Behavior
This section describes how to modify the link loss behavior of devices that use either fibre channel or
iSCSI protocols.
21.16.1. Fibre Channel
If a driver implements the Transport dev_loss_tmo callback, access attempts to a device through
a link will be blocked when a transport problem is detected. To verify if a device is blocked, run the
following command:
cat /sys/block/device/device/state
This command will return blocked if the device is blocked. If the device is operating normally, this
command will return running.
Procedure 21.5. Determining The State of a Remote Port
1. To determine the state of a remote port, run the following command:
cat /sys/class/fc_remote_port/rport-H:B:R/port_state
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http://www.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/5.4/html/DM_Multipath/index.html