Online LUN Detection in RedHat Enterprise Linux
Release:
RedHat Enterprise Linux
Problem:
Detect Newly assigned LUN in RHEL without reboot the server
Solution:
1) Install the required packages
# yum install sysfsutils sg3_utils
2) We need the below parameters to rescan the scsi bus
H – HBA Number
C – Channel on the HBA
T – SCSI target id
L – LUN id
3) We can get the above said parameters using the different command, for me I am using “systool” and “sg_map” command
# systool -c fc_host -v
Class Device = "host3"
Class Device path = "/sys/class/fc_host/host3"
port_name = "0x2100001b32882e82"
Note : In the above sample output class device path is “host3”. So 3 is the HBA number, if dual channel HBA means like the above host4 also will displayed. Here port name is the HBA's wwn id.
# systool -c fc_transport -v
Class Device = "0:0"
Class Device path = "/sys/class/fc_transport/target3:0:0"
port_name = "0x200400a0b84889b5"
Note: In the above command output, class device path is “3:0:0”, that is in the order of “HBA number:channel on HBA:SCSI Target id” (H:C:T). Here port name is the storage's wwpn id.
# sg_map -x
/dev/sg0 0 0 0 0 0
/dev/sg1 0 0 1 0 0
/dev/sg2 0 1 0 0 0 /dev/sda
/dev/sg3 3 0 0 0 0
/dev/sg4 3 0 0 31 0
/dev/sg5 3 0 1 0 0 /dev/sdb
/dev/sg6 3 0 1 1 0 /dev/sdc
/dev/sg7 3 0 2 0 0 /dev/sdd
/dev/sg8 3 0 2 1 0 /dev/sde
Note: In the above command output, first four digits as represents “H C T L” also known as Host, Bus, Target, Lun (H B T L). From this we can identify how many luns are already mapped.
4) Now rescan the SCSI bus using the said parameters
# echo “C T L” > /sys/class/scsi_host/HostH/scan
Note: If u are having dual channel HBA card means scan both the HBA numbers using the above command .
5) Now check with the fdisk command, whether the LUN is detected or not. If not means use the below command
# echo “1” > /sys/class/fc_host/hostH/issue_lip
Note: The above command instruct the driver to rediscover the remote ports. LIP (Loop Initialization Protocol).
6) Now confirm with the fdisk command and use the LUN as usual.
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