How Install and Configure iSCSI Storage server on CentOS 7


In our previous tutorial, we covered how to install and configure iSCSI storage server on Ubuntu 18.04 and in this tutorial, we are going to learn how to implement the same on CentOS 7 and other RHEL derivatives.

In this deployment, we will be using two CentOS 7 servers, one acting as the iSCSI target while the other functions as the iSCSI initiator.

iSCSI target:
IP Address:

iSCSI initiator:
IP Address:

Setting Up the iSCSI Target

To set up an iSCSI target, we need to install an administration tool called targetcli which provides the default interface for managing the target.

   # yum install targetcli -y

After installing targetcli, let us configure iSCSI.

  1. Create the backend storage devices

    We will create two logical volumes each of 200MB to provide the backend storage for setting up the iSCSI target. Ensure that you have enough space on the volume group to be used. In my case, my volume group is dev/centos.

    # lvcreate -L 200M -n lvsan1 /dev/centos
    # lvcreate -L 200M -n lvsan2 /dev/centos

    Launch the targetcli utility by typing targetcli and you are welcomed by targetcli interactive prompt.

    # targetcli
    targetcli shell version 2.1.fb41
    Copyright 2011-2013 by Datera, Inc and others.
    For help on commands, type 'help'.

    Navigate to backstore directory under targetcli and assign the created logical volumes as the backend storage device.

    /> cd backstores/
    /backstores> block/ create iscsi_disk /dev/centos/san1
    Created block storage object iscsi_disk using /dev/centos/san1.

    NB iscsi_disk is the name of the backing storage device. You can call it a name of your choice.

    We can also create a file-backed block device. To do this, navigate to fileio directory and create a 200MiB sized file residing on the home directory.

    /backstores> cd fileio 
    /backstores/fileio> create iscsi_file /home/disk_file 200MiB
    Created fileio iscsi_file with size 209715200
  2. Create an IQN for the iSCSI target

    This will by default create a Target Portal Group. Navigate to iscsi directory and create it.

    /backstores/fileio> cd /
    /> cd iscsi/
    /iscsi> create
    Created target
    Created TPG 1.
    Default portal not created, TPGs within a target cannot share ip:port.
  3. Configure ACLs for the TPG.

    Navigate to ACL directory of the IQN created above, which is under the default TPG directory under created IQN.

    /iscsi> cd
    /iscsi/iqn.20...t00/tpg1/acls> create
    Created Node ACL for

    This creates a node ACL that allows server2 to access the target’s IQN just created.

    Configure CHAP Authentication by creating initiators’ users, that will be allowed to access backend storage, and their passwords.

    /iscsi/iqn.20...t00/tpg1/acls> cd 
    /iscsi/iqn.20...ample:server2> set auth userid=amos
    Parameter userid is now 'amos'.
    /iscsi/iqn.20...ample:server2> set auth password=password
    Parameter password is now 'password'.
  4. Create the LUNs needed to associate a block device with a specific TPG. For our case, we will use iscsi_diskk block and iscsi_file file created above to create a LUN. Any new LUN created will be mapped to each ACL that is associated with the TPG. Navigate to luns directory under TPG directory.
    /iscsi/iqn.20...ample:server2> cd ../../
    /iscsi/iqn.20...target00/tpg1> cd luns 
    /iscsi/iqn.20...t00/tpg1/luns> create /backstores/block/iscsi_disk 
    Created LUN 0.
    Created LUN 0->0 mapping in node ACL
    /iscsi/iqn.20...t00/tpg1/luns> create /backstores/fileio/iscsi_file 
    Created LUN 1.
    Created LUN 1->1 mapping in node ACL
  5. Optionally, to configure a target to offer services on specific address, create a portal for that address. Remember the IP address used must be fixed. To do this, Navigate to portals and create it.
    /iscsi/iqn.20...target00/tpg1> cd portals
    /iscsi/iqn.20.../tpg1/portals> create
    Using default IP port 3260
    Created network portal
  6. Exit the targetcli utility and check whether port 3260 is open.
    # ss -na | grep 3260
    tcp    LISTEN     0      256       *:3260                *:*  
  7. Configure the iSCSI target to be accessed through firewall;
    # firewall-cmd --add-port=3260/tcp --permanent
    # firewall-cmd --reload
  8. Start iSCSI target and enable it to run when the system boots.
    # systemctl enable target
    # systemctl start target

Setting Up the iSCSI Initiator.

Follow these simple steps to configure an iSCSI Initiator.

  1. Install iSCSI Initiator utilities.
    # yum install -y iscsi-initiator-utils

    Edit the file /etc/iscsi/initiatorname.iscsi and add the name of the initiator and restart the iscsid service

    # vim /etc/iscsi/initiatorname.iscsi
     # systemctl restart iscsid

    Configure authentication

    # vim /etc/iscsi/iscsid.conf
    #Uncomment the following line
    node.session.auth.authmethod = CHAP
    # Uncomment these lines and specify the username and password set on the iSCSI target server
     node.session.auth.username = <username>
     node.session.auth.password = <strong-password>

    Save the file and exit.

  2. Discover available targets using the iscsiadm command. When iscsiadm is operating on discovery mode, three arguments are passed:
    • sendtargets type — specifies how to find the targets.
    • portal — tells the iscsiadm the IP address and port to address so as to perform discovery. Default port is 3260.
    • discover — tells the iscsid service to perform a discovery.

    So, to perform an iSCSI discovery, run the command:

    # iscsiadm --m discovery -t sendtargets --p --discover,1
  3. Log into the target using the iscsiadm command.
    # iscsiadm -m node --login 
    Logging in to [iface: default, target:, portal:,3260] (multiple)
    Login to [iface: default, target:, portal:,3260] successful.
  4. Once the connection is established, both session and node details can be checked as follows.
    # iscsiadm -m session -o show 
    tcp: [1],1 (non-flash)
    # iscsiadm --mode node -P 1
                    Iface Name: default
  5. Mounting the iSCSI Devices

    List the available iSCSI devices using the lsscsi command

    # lsscsi
    [0:0:0:0]    cd/dvd  QEMU     QEMU DVD-ROM     2.5+  /dev/sr0 
    [2:0:0:0]    disk    LIO-ORG  sanblock1        4.0   /dev/sda        
    [2:0:0:1]    disk    LIO-ORG  sanblock2        4.0   /dev/sdb        
    [2:0:0:2]    disk    LIO-ORG  sanfile1         4.0   /dev/sdc        
    [3:0:0:0]    disk    LIO-ORG  iscsi_disk       4.0   /dev/sdd 
    [3:0:0:1]    disk    LIO-ORG  iscsi_file       4.0   /dev/sde 

    Our iSCSI device is denoted by /dev/sdd. Create an xfs filesystem on the new iSCSI disk.

    # mkfs.xfs /dev/sdd
    meta-data=/dev/sdd               isize=256    agcount=4, agsize=12800 blks
             =                       sectsz=512   attr=2, projid32bit=1
             =                       crc=0        finobt=0
    data     =                       bsize=4096   blocks=51200, imaxpct=25
             =                       sunit=0      swidth=0 blks
    naming   =version 2              bsize=4096   ascii-ci=0 ftype=0
    log      =internal log           bsize=4096   blocks=853, version=2
             =                       sectsz=512   sunit=0 blks, lazy-count=1
    realtime =none                   extsz=4096   blocks=0, rtextents=0

    Create a mount point say at /mnt/ directory.

    # mkdir /mnt/iscsi_disk

    Use the command blkid to obtain the UUID for the device so we can use in /etc/fstab for mounting.

    # blkid /dev/sdd
    /dev/sdd: UUID="cd65bc73-ef75-41fe-ac78-e5dab9cdc102" TYPE="xfs"

    Edit the /etc/fstab/ file and add the following line

     UUID=cd65bc73-ef75-41fe-ac78-e5dab9cdc102 /mnt/iscsi_disk xfs _netdev  0 2

    Mount all devices and verify.

    # mount -a
    # df -hT
    Filesystem                Type      Size  Used Avail Use% Mounted on
    /dev/mapper/centos-root   xfs       7.6G  1.1G  6.6G  14% /
    devtmpfs                  devtmpfs  487M     0  487M   0% /dev
    tmpfs                     tmpfs     497M     0  497M   0% /dev/shm
    tmpfs                     tmpfs     497M   13M  484M   3% /run
    tmpfs                     tmpfs     497M     0  497M   0% /sys/fs/cgroup
    /dev/vda1                 xfs       497M  125M  373M  26% /boot nfs4      7.6G  1.4G  6.3G  18% /home
    tmpfs                     tmpfs     100M     0  100M   0% /run/user/0
    /dev/sdd                  xfs       197M   11M  187M   6% /mnt/iscsi_disk

    iSCSI device, /dev/sdd is mounted at our mount point, /mnt/iscsi_disk

Big up, you have successfully configured an iSCSI target (server) and shared  a block device to an iSCSI client.
In our next article, we will cover how to automount an iSCSI storage during every boot



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