CentOS 7.x iSCSI initiator client setup

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To use iSCSI drive from a target on a client machine using initiator use following steps:

1. Ensure that package iscsi-initiator-utils is present
2. Ensure that InitiatorName is present in /etc/iscsi/initiatorname.iscsi file
3. Ensure that iscsid service is enabled and running
4. Discover the target using below command

   iscsiadm -m discovery -t st -p 192.168.1.200

   OR

   iscsiadm --mode discovery --type sendtargets --portal 192.168.1.200

5. Login to the discovered target using values from discovery command:

   iscsiadm -m node -T  iqn.2003-01.org.linux-iscsi.iscsi.x8664:sn.4f81e28c9c7d -p 192.168.1.200 -l

   Other option is to run discovery with "-l" so that automatic login to all discovered luns is done.

   iscsiadm --mode discovery --type sendtargets --portal 192.168.1.200 -l

6. Check status of current iscsi sessions on server using (Only in case of Linux target iscsi server):

   targetcli sessions

7. On client check sessions using:

   iscsiadm -m session

8. On client disk should be visible using "fdisk -l". However if you want to distinguish between various disks (Say if you have 3 disks all three of 5 GB) then you can look at "/dev/disk/by-path/" devices. In this folder devices are named based on iqn so it is easy to select a disk/lun based on iqn.
9. If client was already logged in and a new disk is shared it may not become visible directly. To see new disks either
   • Disconnect session as explained in next step and connect again
   • Or rescan SCSI devices using:

     echo "- - -" > /sys/class/scsi_host/host<n>/scan

     where <n> should vary based on folders visible under /sys/class/scsi_host. We need to scan all hosts once using above command.

10. On client disconnect session using:

    iscsiadm -m session -r <session_number> -u

    where session number is listed using 'iscsiadm -m session' command

11. On client delete unwanted or wrong discovered sessions using:

    iscsiadm -m discovery
    iscsiadm -m discovery -p 192.168.122.85:3260 -o delete

    If you do not do this and if iscsi server is not available during reboot then system wont boot properly with following lines in /var/log/messages

    Sep 27 20:08:38 barjatiyarklp iscsid: cannot make a connection to 192.168.122.85:3260 (-1,101)

    To fix such a system you would have to boot in single mode and use iscsiadm command with -o delete as explained above

12. On client various information about iSCSI target is cached in sub-folders inside /var/lib/iscsi folder.

Refer:

• https://geekpeek.net/rescan-scsi-bus-on-linux-system/

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