Showing posts with label rescan scsi bus linux. Show all posts
Showing posts with label rescan scsi bus linux. Show all posts

Solved: How to scan new LUNs in Redhat Linux

In this post  we will discuss how to scan new LUNs allocated by storage team to a Redhat Linux system.
There are two ways of scanning the LUNs
Method 1:-
Find how many SCSI bus controllers you have

  • Go to directory /sys/class/scsi_host/  and list it’s contents.

cd /sys/class/scsi_host/ 
[root@scsi_host]# ls
host0 host1 host2
  • Here we can see we have three SCSI bus controllers. So in below command replace hostX with these directory names.
Run the Command ,
echo "- - -" > /sys/class/scsi_host/hostX/scan 
[root@cloudvedas]# echo "- - -" > /sys/class/scsi_host/host0/scan
[root@cloudvedas]# echo "- - -" > /sys/class/scsi_host/host1/scan
[root@cloudvedas]# echo "- - -" > /sys/class/scsi_host/host2/scan
[root@cloudvedas]# echo "- - -" > /sys/class/scsi_host/host3/scan
TIP:- Here the “- – -” denotes CxTxDx i.e. Channel(controller) , Target ID and Disk or LUN number. This is asked in Linux Admin Interviews also.
  • Repeat the above step for all three directories.
If you have FC HBA in the system you can follow the steps as below:-
  • First check number of FC controllers in your system
#ls /sys/class/fc_hosthost0 host1 host2
  • To scan FC LUNs execute commands as
echo "1" > /sys/class/fc_host/host0/issue_lip
echo "1" > /sys/class/fc_host/host1/issue_lip
echo "1" > /sys/class/fc_host/host2/issue_lip

Tip :- Here echo “1” operation performs a Loop Initialization Protocol (LIP) and then scans the interconnect and causes the SCSI layer to be updated to reflect the devices currently on the bus. A LIP is, essentially, a bus reset,  and will cause device addition and removal. This procedure is necessary to configure a new SCSI target on a Fibre Channel interconnect. Bear in mind that issue_lip is an asynchronous operation.
  • Verify if the new disk is visible now
fdisk -l |egrep '^Disk' |egrep -v 'dm-'
Method 2 :-
  • Next method is to scan using SG3 utility. You can install it using
yum install sg3_utils
  • Once installed  run the command