Scanning SCSI Bus and HBA Devices in Linux

How to scan HBA’s to acquire newly added storage:

Loop Initialization Protocol (issue_lip): Loop Initialization Protocol is a method to perform bus reset which scan the scsi bus and updates the scsi layer to reflect all the scsi devices. This is a asynchronous operation and may take longer time to complete. Usually after executing the command to trigger issue_lip, you would get a command prompt immediately, but in actual it might take up longer time to complete the bus scan.

Loop Initialization Protocol method to scan the HBA’s can cause delay and I/O timeouts if the HBA/Device is in use and can also remove devices unexpectedly. Hence performing the scan using this method is not recommended on any production server where the SAN Devices are already configured in use. This type of scan is recommended on a newly built server to scan all the LUNS/Devices.

To perform the bus scan using this method, execute the following command as root.

echo “1″ > /sys/class/fc_host/host*/issue_lip // this command will scan all the HBA’s

If you want to scan any specific HBA, then execute the command as below

echo “1″ > /sys/class/fc_host/hostN/issue_lip //replace N with the number of HBA to scan

Scanning specific device/path :

If you have a running server where you need to scan specific device or a path to the device, it is not recommended to use issue_lip method and you should use the below method to scan for the updated device information.

To scan a specific device/lun, you need the following information at minimum.

1. WWNN Number of the HBA to scan

2. Lun number (which is assigned from SAN)

Once you have the above mentioned information, you can identify the HBA number, HBA Channel and SCSI Target ID information by executing the following command.

grep 1111111111111111 /sys/class/fc_transport/*/node_name //replace ’1111111111111111′ with actual WWNN Number.

This command would display output as below

/sys/class/fc_transport/target4:0:1/node_name:0×5006016090203181

In this case, the HBA number (Host) is 4, HBA Channel is 0 and SCSI Target id is 1. If the Lun Number is 11, execute the following command to scan this device.

echo “0 1 11″ >/sys/class/scsi_host/host4/scan //here 4 is the HBA Number.

If you do not have the HBA Number, HBA Channel, SCSI Target ID or Lun ID Information, and wanted to scan all devices on specific HBA, execute the following command.

echo “- – -” > /sys/class/scsi_host/hostN/scan //replace N with the HBA Number.

Cheers !!

Vaibhav