Table of Contents

Introduction

iSCSI or Internet Small Computer System is a block-level storage solution shares the disks over the network. It depends on the network and strictly recommend to use high throughput interfaces. In iSCSI, we can create various types of iSCSI devices as a fileio or using block devices and logical volumes then present them as targets.

In a small production environment, we are good to use with software iSCSI. However, in a critical environment with high load required physical HBA card which will provide high performance. In this guide, we are about to perform installing and configuring software iSCSI server and client on top of Red Hat Enterprise Linux 8.

IQN is a unique name to identify the SCSI targets.
Target is the server-side setup available for Initiator.
LUN – Logical unit number

Let start to configure the iSCSI server and client set up in a test environment for demonstration purpose.

iSCSI Storage Target Setup

Server IP       : 192.168.107.225
Server Hostname : linuxsysadmins-iSCSI-srv
Server IQN      : iqn.2019-04.com.linuxsysadmins.com:tgt0
Port No required: 3260

Installing iSCSI Package

Search for iSCSI server package to start the installation. The targetcli package coming from AppStream repository in Red Hat Enterprise Linux 8 to know how to use and work with AppStream click here to read.

# dnf search targetcli
# yum search targetcli

Install iSCSI server package “targetcli” using DNF or yum.

# dnf install targetcli -y
# yum install targetcli -y

The output of installation will be similar to below by resolving all required dependencies.

[root@linuxsysadmins-iSCSI-srv ~]# dnf install targetcli -y
 Updating Subscription Management repositories.
 Last metadata expiration check: 0:10:40 ago on Tue 02 Apr 2019 10:57:50 PM +04.
 Dependencies resolved.
  Package                            Arch              Version                        Repository            Size
 Installing:
  targetcli                          noarch            2.1.fb49-1.el8                 AppStream             73 k
 Installing dependencies:
  cairo                              x86_64            1.15.12-2.el8                  AppStream            721 k
  cairo-gobject                      x86_64            1.15.12-2.el8                  AppStream             33 k
  libX11                             x86_64            1.6.7-1.el8                    AppStream            612 k
  libX11-common                      noarch            1.6.7-1.el8                    AppStream            157 k
  libXau                             x86_64            1.0.8-13.el8                   AppStream             36 k
  libXext                            x86_64            1.3.3-9.el8                    AppStream             45 k
  libXrender                         x86_64            0.9.10-7.el8                   AppStream             33 k
  libxcb                             x86_64            1.13-5.el8                     AppStream            230 k
  pixman                             x86_64            0.34.0-9.el8                   AppStream            256 k
  python3-cairo                      x86_64            1.16.3-6.el8                   AppStream             90 k
  python3-gobject                    x86_64            3.28.3-1.el8                   AppStream             25 k
  dejavu-fonts-common                noarch            2.35-6.el8                     BaseOS                74 k
  dejavu-sans-fonts                  noarch            2.35-6.el8                     BaseOS               1.5 M
  fontconfig                         x86_64            2.13.1-2.el8                   BaseOS               274 k
  fontpackages-filesystem            noarch            1.44-22.el8                    BaseOS                16 k
  python3-configshell                noarch            1:1.1.fb25-1.el8               BaseOS                74 k
  python3-kmod                       x86_64            0.9-20.el8                     BaseOS                90 k
  python3-rtslib                     noarch            2.1.fb69-2.el8                 BaseOS               100 k
  python3-urwid                      x86_64            1.3.1-4.el8                    BaseOS               783 k
  target-restore                     noarch            2.1.fb69-2.el8                 BaseOS                23 k
 Transaction Summary
 Install  21 Packages
 Total size: 5.1 M
 Installed size: 17 M
   Running scriptlet: targetcli-2.1.fb49-1.el8.noarch                                                      21/21 
   Running scriptlet: fontconfig-2.13.1-2.el8.x86_64                                                       21/21 
   Verifying        : cairo-1.15.12-2.el8.x86_64                                                            1/21 
   Verifying        : cairo-gobject-1.15.12-2.el8.x86_64                                                    2/21 
   Verifying        : libX11-1.6.7-1.el8.x86_64                                                             3/21 
   Verifying        : libX11-common-1.6.7-1.el8.noarch                                                      4/21 
   Verifying        : libXau-1.0.8-13.el8.x86_64                                                            5/21 
   Verifying        : libXext-1.3.3-9.el8.x86_64                                                            6/21 
   Verifying        : libXrender-0.9.10-7.el8.x86_64                                                        7/21 
   Verifying        : libxcb-1.13-5.el8.x86_64                                                              8/21 
   Verifying        : pixman-0.34.0-9.el8.x86_64                                                            9/21 
   Verifying        : python3-cairo-1.16.3-6.el8.x86_64                                                    10/21 
   Verifying        : python3-gobject-3.28.3-1.el8.x86_64                                                  11/21 
   Verifying        : targetcli-2.1.fb49-1.el8.noarch                                                      12/21 
   Verifying        : dejavu-fonts-common-2.35-6.el8.noarch                                                13/21 
   Verifying        : dejavu-sans-fonts-2.35-6.el8.noarch                                                  14/21 
   Verifying        : fontconfig-2.13.1-2.el8.x86_64                                                       15/21 
   Verifying        : fontpackages-filesystem-1.44-22.el8.noarch                                           16/21 
   Verifying        : python3-configshell-1:1.1.fb25-1.el8.noarch                                          17/21 
   Verifying        : python3-kmod-0.9-20.el8.x86_64                                                       18/21 
   Verifying        : python3-rtslib-2.1.fb69-2.el8.noarch                                                 19/21 
   Verifying        : python3-urwid-1.3.1-4.el8.x86_64                                                     20/21 
   Verifying        : target-restore-2.1.fb69-2.el8.noarch                                                 21/21 
 Installed:
   targetcli-2.1.fb49-1.el8.noarch                         cairo-1.15.12-2.el8.x86_64                            
   cairo-gobject-1.15.12-2.el8.x86_64                      libX11-1.6.7-1.el8.x86_64                             
   libX11-common-1.6.7-1.el8.noarch                        libXau-1.0.8-13.el8.x86_64                            
   libXext-1.3.3-9.el8.x86_64                              libXrender-0.9.10-7.el8.x86_64                        
   libxcb-1.13-5.el8.x86_64                                pixman-0.34.0-9.el8.x86_64                            
   python3-cairo-1.16.3-6.el8.x86_64                       python3-gobject-3.28.3-1.el8.x86_64                   
   dejavu-fonts-common-2.35-6.el8.noarch                   dejavu-sans-fonts-2.35-6.el8.noarch                   
   fontconfig-2.13.1-2.el8.x86_64                          fontpackages-filesystem-1.44-22.el8.noarch            
   python3-configshell-1:1.1.fb25-1.el8.noarch             python3-kmod-0.9-20.el8.x86_64                        
   python3-rtslib-2.1.fb69-2.el8.noarch                    python3-urwid-1.3.1-4.el8.x86_64                      
   target-restore-2.1.fb69-2.el8.noarch                   
 Complete!
 [root@linuxsysadmins-iSCSI-srv ~]#

Adding Firewall Rule

From RHEL 7.x all the RHEL based operating systems will come with iSCSI-target firewallD service. Instead of adding a port we required to add the service.

# cat /usr/lib/firewalld/services/iscsi-target.xml

A simple XML format firewall service will make our life easier.

[root@linuxsysadmins-iSCSI-srv ~]# cat /usr/lib/firewalld/services/iscsi-target.xml 
<?xml version="1.0" encoding="utf-8"?>
<service>
  <short>iSCSI target;/short>>
  <description>Internet SCSI target is a storage resource located on an iSCSI server.</description>
  <port protocol="tcp" port="3260"/>
  <port protocol="udp" port="3260"/>
</service>
[root@linuxsysadmins-iSCSI-srv ~]#

Let’s add the required service so that we will be good at opening the required ports.

# firewall-cmd --add-service=iscsi-target --permanent
# firewall-cmd --reload
# firewall-cmd --list-all

To make sure the firewall in place verifies as shown below. Once the iSCSI service started we need to list the port and check whether it’s listening.

[root@linuxsysadmins-iSCSI-srv ~]# firewall-cmd --add-service=iscsi-target --permanent
 success
 [root@linuxsysadmins-iSCSI-srv ~]# firewall-cmd --reload
 success
 [root@linuxsysadmins-iSCSI-srv ~]# firewall-cmd --list-all
 public
   target: default
   icmp-block-inversion: no
   interfaces: 
   sources: 
   services: cockpit dhcpv6-client iscsi-target ssh
   ports: 
   protocols: 
   masquerade: no
   forward-ports: 
   source-ports: 
   icmp-blocks: 
   rich rules: 
 [root@linuxsysadmins-iSCSI-srv ~]#

Start the “target” service

# systemctl start target
# systemctl enable target
# systemctl status target

Verify target service status by running above command.

[root@linuxsysadmins-iSCSI-srv ~]# systemctl start target
 [root@linuxsysadmins-iSCSI-srv ~]# 
 [root@linuxsysadmins-iSCSI-srv ~]# systemctl enable target
 Created symlink /etc/systemd/system/multi-user.target.wants/target.service → /usr/lib/systemd/system/target.service. 
 [root@linuxsysadmins-iSCSI-srv ~]# systemctl status target
 ● target.service - Restore LIO kernel target configuration
    Loaded: loaded (/usr/lib/systemd/system/target.service; enabled; vendor preset: disabled)
    Active: active (exited) since Tue 2019-04-02 23:10:04 +04; 1min 20s ago
  Main PID: 9908 (code=exited, status=0/SUCCESS)
     Tasks: 0 (limit: 11368)
    Memory: 0B
    CGroup: /system.slice/target.service
 Apr 02 23:10:04 linuxsysadmins-iSCSI-srv systemd[1]: Starting Restore LIO kernel target configuration…
 Apr 02 23:10:04 linuxsysadmins-iSCSI-srv target[9908]: No saved config file at /etc/target/saveconfig.json, ok,>
 Apr 02 23:10:04 linuxsysadmins-iSCSI-srv systemd[1]: Started Restore LIO kernel target configuration.
 [root@linuxsysadmins-iSCSI-srv ~]#

At last, let us verify the port using “netstat or “ss” command before moving forward.

# netstat -tnlp | grep 3260
# ss -napt | grep 3260

The enabled port for the target is Up and we are good to continue with the setup.

[root@linuxsysadmins-iSCSI-srv ~]# netstat -tnlp | grep 3260
 tcp        0      0 0.0.0.0:3260            0.0.0.0:*               LISTEN      -                   
 [root@linuxsysadmins-iSCSI-srv ~]#
 [root@linuxsysadmins-iSCSI-srv ~]# ss -napt | grep 3260
 LISTEN  0        256                   0.0.0.0:3260      0.0.0.0:*                                                                                       
 [root@linuxsysadmins-iSCSI-srv ~]#

Start Configuring iSCSI Target

To start the iSCSI target configuration we need to run the “targetcli” command from a privileged account.

# targetcli

Let’s go through each step, Once we log-in to the target command line press TAB key twice to know all the available commands and options in the targetcli.

Navigate to backstores/block and start to create the back store using our 2 TB physical disk /dev/sdb.

/backstores/block> create name=LUN0 dev=/dev/sdb

In case, if we required to create a 1GB of fileio back store, use below command

cd ../fileio/ create file01 /data/disk1 1G

Then back to / directory of targetcli or navigate to iscsi path using cd ../../iscsi.

cd ../../iscsi

Create an IQN for the target, When we are creating the IQN it will manage to create the TPG under this IQN.

create iqn.2019-04.com.linuxsysadmins.com:tgt0

From created IQN navigate to LUNs and map it.

cd iqn.2019-04.com.linuxsysadmins.com:tgt0/tpg1/luns

Create the LUN

create /backstores/block/LUN0

Navigate to ACL under the target and create one for the client nodes.

cd ../acls

Allow the client machine by creating an ACL.

create iqn.2019-04.com.linuxsysadmins:client01

Navigate to created ACL and set and username and password for CHAP authentication

cd iqn.2019-04.com.linuxsysadmins:client01/

Choose any username and password

set auth userid=linuxsysadmins
set auth password=sysadmins@123

The creating portal will be automatically done while we create with IQN.

To make all changes persistent navigate to root directory of targetcli and run the command “saveconfig“ to save the configuration in JSON format. And type “exit” to come out of targetcli.

cd ../../../../
saveconfig
exit

Output from Terminal

The RAW output from command line is below for your reference.

[root@linuxsysadmins-iSCSI-srv ~]# targetcli
 targetcli shell version 2.1.fb49
 Copyright 2011-2013 by Datera, Inc and others.
 For help on commands, type 'help'.
 /> 
 /> ls
 o- / …………………………………………………………………………………………………………. […]
   o- backstores ……………………………………………………………………………………………….. […]
   | o- block …………………………………………………………………………………….. [Storage Objects: 0]
   | o- fileio ……………………………………………………………………………………. [Storage Objects: 0]
   | o- pscsi …………………………………………………………………………………….. [Storage Objects: 0]
   | o- ramdisk …………………………………………………………………………………… [Storage Objects: 0]
   o- iscsi ……………………………………………………………………………………………… [Targets: 0]
   o- loopback …………………………………………………………………………………………… [Targets: 0]
 /> 
 /> cd backstores/block 
 /backstores/block> 
 /backstores/block> create name=LUN0 dev=/dev/sdb 
 Created block storage object LUN0 using /dev/sdb.
 /backstores/block> 
 /backstores/block> ls
 o- block ………………………………………………………………………………………… [Storage Objects: 1]
   o- LUN0 ……………………………………………………………………. [/dev/sdb (2.0TiB) write-thru deactivated]
     o- alua …………………………………………………………………………………………. [ALUA Groups: 1]
       o- default_tg_pt_gp ………………………………………………………………… [ALUA state: Active/optimized]
 /backstores/block> 
 /backstores/block> cd ../..
 /> 
 /> cd iscsi 
 /iscsi> 
 /iscsi> create iqn.2019-04.com.linuxsysadmins.com:tgt0
 Created target iqn.2019-04.com.linuxsysadmins.com:tgt0.
 Created TPG 1.
 Global pref auto_add_default_portal=true
 Created default portal listening on all IPs (0.0.0.0), port 3260.
 /iscsi> 
 /iscsi> ls
 o- iscsi ……………………………………………………………………………………………….. [Targets: 1]
   o- iqn.2019-04.com.linuxsysadmins.com:tgt0 ………………………………………………………………….. [TPGs: 1]
     o- tpg1 ……………………………………………………………………………………. [no-gen-acls, no-auth]
       o- acls ……………………………………………………………………………………………… [ACLs: 0]
       o- luns ……………………………………………………………………………………………… [LUNs: 0]
       o- portals ………………………………………………………………………………………… [Portals: 1]
         o- 0.0.0.0:3260 …………………………………………………………………………………………. [OK]
 /iscsi> 
 /iscsi> cd iqn.2019-04.com.linuxsysadmins.com:tgt0/tpg1/luns 
 /iscsi/iqn.20…gt0/tpg1/luns> ls
 o- luns …………………………………………………………………………………………………… [LUNs: 0]
 /iscsi/iqn.20…gt0/tpg1/luns> create /backstores/block/LUN0 
 Created LUN 0.
 /iscsi/iqn.20…gt0/tpg1/luns> ls
 o- luns …………………………………………………………………………………………………… [LUNs: 1]
   o- lun0 ……………………………………………………………………. [block/LUN0 (/dev/sdb) (default_tg_pt_gp)]
 /iscsi/iqn.20…gt0/tpg1/luns> cd ../acls 
 /iscsi/iqn.20…gt0/tpg1/acls> 
 /iscsi/iqn.20…gt0/tpg1/acls> create iqn.2019-04.com.linuxsysadmins:client01
 Created Node ACL for iqn.2019-04.com.linuxsysadmins:client01
 Created mapped LUN 0.
 /iscsi/iqn.20…gt0/tpg1/acls> ls
 o- acls …………………………………………………………………………………………………… [ACLs: 1]
   o- iqn.2019-04.com.linuxsysadmins:client01 ………………………………………………………… [Mapped LUNs: 1]
     o- mapped_lun0 ……………………………………………………………………………… [lun0 block/LUN0 (rw)]
 /iscsi/iqn.20…gt0/tpg1/acls> cd iqn.2019-04.com.linuxsysadmins:client01/
 /iscsi/iqn.20….com:client01> 
 /iscsi/iqn.20….com:client01> ls
 o- iqn.2019-04.com.linuxsysadmins:client01 ………………………………………………………….. [Mapped LUNs: 1]
   o- mapped_lun0 ……………………………………………………………………………….. [lun0 block/LUN0 (rw)]
 /iscsi/iqn.20….:client01> set auth userid=linuxsysadmins
 Parameter userid is now 'linuxsysadmins'.
 /iscsi/iqn.20….:client01> set auth password=sysadmins@123
 Parameter password is now 'sysadmins@123'.
 /iscsi/iqn.20….:client01> 
 /iscsi/iqn.20….:client01> cd ../../../../
 /iscsi> cd ..
 /> saveconfig 
 Configuration saved to /etc/target/saveconfig.json
 />
 /> 
 /> ls
 o- / …………………………………………………………………………………………………………. […]
   o- backstores ……………………………………………………………………………………………….. […]
   | o- block …………………………………………………………………………………….. [Storage Objects: 1]
   | | o- LUN0 ………………………………………………………………….. [/dev/sdb (2.0TiB) write-thru activated]
   | |   o- alua ……………………………………………………………………………………… [ALUA Groups: 1]
   | |     o- default_tg_pt_gp …………………………………………………………….. [ALUA state: Active/optimized]
   | o- fileio ……………………………………………………………………………………. [Storage Objects: 0]
   | o- pscsi …………………………………………………………………………………….. [Storage Objects: 0]
   | o- ramdisk …………………………………………………………………………………… [Storage Objects: 0]
   o- iscsi ……………………………………………………………………………………………… [Targets: 1]
   | o- iqn.2019-04.com.linuxsysadmins.com:tgt0 ………………………………………………………………… [TPGs: 1]
   |   o- tpg1 ………………………………………………………………………………….. [no-gen-acls, no-auth]
   |     o- acls ……………………………………………………………………………………………. [ACLs: 1]
   |     | o- iqn.2019-04.com.linuxsysadmins:client01 …………………………………………………. [Mapped LUNs: 1]
   |     |   o- mapped_lun0 ………………………………………………………………………. [lun0 block/LUN0 (rw)]
   |     o- luns ……………………………………………………………………………………………. [LUNs: 1]
   |     | o- lun0 …………………………………………………………….. [block/LUN0 (/dev/sdb) (default_tg_pt_gp)]
   |     o- portals ………………………………………………………………………………………. [Portals: 1]
   |       o- 0.0.0.0:3260 ……………………………………………………………………………………….. [OK]
   o- loopback …………………………………………………………………………………………… [Targets: 0]
 /> 
 /> exit
 Global pref auto_save_on_exit=true
 Last 10 configs saved in /etc/target/backup/.
 Configuration saved to /etc/target/saveconfig.json

iSCSI after creating LUN — Listing a created iSCSI LUN

That’s it we have completed with configuring iSCSI Target in RHEL 8 server. The same steps are applied for RHEL 7.x servers as-well.

Continue to setup iSCSI client side configuration.

iSCSI Client-Side Configurations

Client-side configuration is super easy and make sure to use the man page effectively.

Client             : 192.168.107.130
Server Name        : linuxsysadmins-client
Initiator IQN      : iqn.2019-04.com.linuxsysadmins:client01

Install the iSCSI initiator package using DNF or yum.

# dnf search iscsi-initiator-utils
# dnf install iscsi-initiator-utils -y
# yum search iscsi-initiator-utils
# yum install iscsi-initiator-utils -y

Very fewer numbers of packages and dependencies are resolved for client setup.

[root@linuxsysadmins-client ~]# dnf install iscsi-initiator-utils -y
 Updating Subscription Management repositories.
 Last metadata expiration check: 0:01:50 ago on Tue 02 Apr 2019 09:11:25 PM EDT.
 Dependencies resolved.
 Package                          Arch     Version                         Repository
                                                                                      Size
 Installing:
  iscsi-initiator-utils            x86_64   6.2.0.876-5.gitf3c8e90.el8      BaseOS   371 k
 Installing dependencies:
  iscsi-initiator-utils-iscsiuio   x86_64   6.2.0.876-5.gitf3c8e90.el8      BaseOS    98 k
  isns-utils-libs                  x86_64   0.97-6.el8                      BaseOS   105 k
 Transaction Summary
 Install  3 Packages
 Total size: 574 k
 Installed size: 2.5 M
 Downloading Packages:
 Installed:
   iscsi-initiator-utils-6.2.0.876-5.gitf3c8e90.el8.x86_64                                 
   iscsi-initiator-utils-iscsiuio-6.2.0.876-5.gitf3c8e90.el8.x86_64                        
   isns-utils-libs-0.97-6.el8.x86_64                                                       
 Complete!
 [root@linuxsysadmins-client ~]#

During the target server setup, we have created ACL for IQN “iqn.2019-04.com.linuxsysadmins:client01” so we need to use the same in client-side. Replace the existing initiator name with below one.

# vi /etc/iscsi/initiatorname.iscsi
iqn.2019-04.com.linuxsysadmins:client01

ACL for the target has been defined with user authentication so its time to append them in the conf file. Edit the iscsid.conf and navigate to line number 58, 62, 63 and make sure to change the required parameters as shown below.

# vi +58 /etc/iscsi/iscsid.conf

Un-comment the line number 58 defined for session required “auth.authmethod“. By following un-comment the credentials line and replace “username” and “password” with our credentials.

#node.session.auth.authmethod = CHAP
#node.session.auth.username = username
#node.session.auth.password = password
                To 
node.session.auth.authmethod = CHAP
node.session.auth.username = linuxsysadmins
node.session.auth.password = sysadmins@123

Once completed with configuring the parameters under iscsid.conf start the iSCSI initiator service.

# systemctl start iscsi
# systemctl status iscsi

Discovering iSCSI storage

Now it’s time to discover the iSCSI target. Using the man page grab the required commands with option and argument. To discover and perform a log-in the “iscsiadmin” command comes with long options and argument. Run the manual and navigate to the end of the man page using “SHIFT+G” you will find the example as shown below, Just we need to replace the server information and start the discovery.

# man iscsiadm

Replace the IP of iSCSI server after “–portal” as shown below.

# iscsiadm --mode discoverydb --type sendtargets --portal 192.168.107.225 --discover

Once discovered we will get the target details as follows.

[root@linuxsysadmins-client ~]# iscsiadm --mode discoverydb --type sendtargets --portal 192.168.107.225 --discover
 192.168.107.225:3260,1 iqn.2019-04.com.linuxsysadmins.com:tgt0

Now it’s time to login into the iSCSI storage from our initiator. Replace the default IQN with discovered one and try to log-in.

# iscsiadm --mode node --targetname iqn.2019-04.com.linuxsysadmins.com:tgt0 --portal 192.168.107.225 --login

 [root@linuxsysadmins-client ~]#
 [root@linuxsysadmins-client ~]# iscsiadm --mode node --targetname iqn.2019-04.com.linuxsysadmins.com:tgt0 --portal 192.168.107.225 --login
 Logging in to iface: default, target: iqn.2019-04.com.linuxsysadmins.com:tgt0, portal: 192.168.107.225,3260
 Login to [iface: default, target: iqn.2019-04.com.linuxsysadmins.com:tgt0, portal: 192.168.107.225,3260] successful.
 [root@linuxsysadmins-client ~]#

In case if you required to check the session and node information of target we can use below commands.

# iscsiadm --mode session
# iscsiadm --mode node

Session and node information as follows.

[root@linuxsysadmins-client ~]# iscsiadm --mode node
 192.168.107.225:3260,1iqn.2019-04.com.linuxsysadmins.com:tgt0
 [root@linuxsysadmins-client ~]# 
 [root@linuxsysadmins-client ~]# iscsiadm --mode session 
 tcp: [4] 192.168.107.225:3260,1 iqn.2019-04.com.linuxsysadmins.com:tgt0 (non-flash)
 [root@linuxsysadmins-client ~]# 
 [root@linuxsysadmins-client ~]#

Monitoring logs

A successful login will get the output similar to below. To get more information it’s good to do a tail on “/var/log/messages“.

[root@linuxsysadmins-client ~]# tail -f /var/log/messages
 Apr  2 22:22:12 linuxsysadmins-client kernel: scsi host32: iSCSI Initiator over TCP/IP
 Apr  2 22:22:12 linuxsysadmins-client kernel: scsi 32:0:0:0: Direct-Access     LIO-ORG  LUN0             4.0  PQ: 0 ANSI: 5
 Apr  2 22:22:12 linuxsysadmins-client kernel: scsi 32:0:0:0: alua: supports implicit and explicit TPGS
 Apr  2 22:22:12 linuxsysadmins-client kernel: scsi 32:0:0:0: alua: device naa.600140513e6bdd6cefc417388e3c4d34 port group 0 rel port 1
 Apr  2 22:22:12 linuxsysadmins-client kernel: scsi 32:0:0:0: Attached scsi generic sg1 type 0
 Apr  2 22:22:12 linuxsysadmins-client kernel: sd 32:0:0:0: alua: transition timeout set to 60 seconds
 Apr  2 22:22:12 linuxsysadmins-client kernel: sd 32:0:0:0: alua: port group 00 state A non-preferred supports TOlUSNA
 Apr  2 22:22:12 linuxsysadmins-client kernel: sd 32:0:0:0: [sda] 4294967296 512-byte logical blocks: (2.20 TB/2.00 TiB)
 Apr  2 22:22:12 linuxsysadmins-client kernel: sd 32:0:0:0: [sda] Write Protect is off
 Apr  2 22:22:12 linuxsysadmins-client kernel: sd 32:0:0:0: [sda] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA
 Apr  2 22:22:12 linuxsysadmins-client kernel: sd 32:0:0:0: [sda] Attached SCSI disk
 Apr  2 22:22:13 linuxsysadmins-client iscsid[940]: Could not set session4 priority. READ/WRITE throughout and latency could be affected.
 Apr  2 22:22:13 linuxsysadmins-client iscsid[940]: Connection4:0 to [target: iqn.2019-04.com.linuxsysadmins.com:tgt0, portal: 192.168.107.225,3260] through [iface: default] is operational now

Listing the iSCSI disks

Once we login to iSCSI storage we will get a SAN disk in our server. To list the new disk we can use any one of below commands.

# lsiscsi -d

Output as follows:

[root@linuxsysadmins-client ~]# lsscsi -d
 [3:0:0:0]    cd/dvd  NECVMWar VMware SATA CD01 1.00  /dev/sr0 [11:0]
 [32:0:0:0]   disk    LIO-ORG  LUN0             4.0   /dev/sda [8:0]
 [N:0:0:1]    disk    VMware Virtual NVMe Disk__1                /dev/nvme0n1 [259:0]
 [root@linuxsysadmins-client ~]#
 [root@linuxsysadmins-client ~]# lsblk --scsi
 NAME HCTL       TYPE VENDOR   MODEL             REV TRAN
 sda  32:0:0:0   disk LIO-ORG  LUN0             4.0  iscsi
 sr0  3:0:0:0    rom  NECVMWar VMware SATA CD01 1.00 sata
 [root@linuxsysadmins-client ~]#

Listing all available block devices and it’s UUID using “blkid“.

# lsblk
# lsblk --scsi
# blkid /dev/sda

Listing all available block devices.

[root@linuxsysadmins-client ~]# lsblk 
 NAME          MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
 sda             8:0    0    2T  0 disk 
 sr0            11:0    1  6.5G  0 rom  
 nvme0n1       259:0    0   20G  0 disk 
 |-nvme0n1p1   259:1    0    1G  0 part /boot
 -nvme0n1p2   259:2    0   19G  0 part    |-rhel-root 253:0    0   17G  0 lvm  / -rhel-swap 253:1    0    2G  0 lvm  [SWAP]
 [root@linuxsysadmins-client ~]#
    
 [root@linuxsysadmins-client ~]# blkid /dev/sda 
 /dev/sda: UUID="19367bf8946c48ac9ac68662ea46b14e" POOL_UUID="9fa5b3250f51484d91faf0bc78138fdb" BLOCKDEV_SECTORS="4294967296" BLOCKDEV_INITTIME="1549484384" TYPE="stratis"
 [root@linuxsysadmins-client ~]#

In any case, if we required more verbose information about the session use “-m” or “–mode” and specify the mode (session, node, host iface and discoverydb) print (-P) the session tree format with more verbose.

# iscsiadm -m session -P 3

The output of session information in print level 3.

[root@linuxsysadmins-client ~]# iscsiadm -m session -P 3
 iSCSI Transport Class version 2.0-870
 version 6.2.0.876-5
 Target: iqn.2019-04.com.linuxsysadmins.com:tgt0 (non-flash)
     Current Portal: 192.168.107.225:3260,1
     Persistent Portal: 192.168.107.225:3260,1
                  Interface:         
         Iface Name: default
         Iface Transport: tcp
         Iface Initiatorname: iqn.2019-04.com.linuxsysadmins.com:client01
         Iface IPaddress: 192.168.107.130
         Iface HWaddress: default
         Iface Netdev: default
         SID: 4
         iSCSI Connection State: LOGGED IN
         iSCSI Session State: LOGGED_IN
         Internal iscsid Session State: NO CHANGE
         *
         Timeouts:
         *
         Recovery Timeout: 120
         Target Reset Timeout: 30
         LUN Reset Timeout: 30
         Abort Timeout: 15
         
         CHAP:
         
         username: linuxsysadmins
         password: 
         username_in: 
         password_in: 
                  Negotiated iSCSI params:         
         HeaderDigest: None
         DataDigest: None
         MaxRecvDataSegmentLength: 262144
         MaxXmitDataSegmentLength: 262144
         FirstBurstLength: 65536
         MaxBurstLength: 262144
         ImmediateData: Yes
         InitialR2T: Yes
         MaxOutstandingR2T: 1
                  Attached SCSI devices:         
         Host Number: 32 State: running
         scsi32 Channel 00 Id 0 Lun: 0
             Attached scsi disk sda      State: running
 [root@linuxsysadmins-client ~]#

Logout an iSCSI node

We are covering only for information on how to log out a session. But in a production environment, this should not be performed until unless we required for some troubleshooting during an Incident, If do so it will end up in data loss and cause more disaster.

To logout the session we required to replace the “–login” with “–logout“.

# iscsiadm --mode node --targetname iqn.2019-04.com.linuxsysadmins.com:tgt0 --portal 192.168.107.225:3260 --logout

Troubleshooting iSCSI

It’s good to know where iSCSI portals discovery information and node information are stored. This will help during iSCSI troubleshooting.

# cd /var/lib/iscsi

Partitioning and Creating file System

To partition and creating a file system on top of any disks kindly refer below articles.

FDISK to partition the disks in Linux

Are you looking to create a Logical volume or VDO on top of above 2 TB LUN? Have a look at below guides.

Conclusion

We have seen how to set up iSCSI Storage by installing and configuring iSCSI Target (Server) and get the SAN disks in an Initiator (Client). iSCSI is a poor man’s SAN which easier to set up in any flavor of Linux servers. Let see you soon in the next guide, Subscribe to our newsletter and receive our updates once we posted. Your comments are most welcome, kindly let us know if any correction needs to be updated.

jos on How to Configure Sudo email alertMarch 4, 2022
Hi! Some way to send commands write as root by email? Thanks!
paul on Monitoring Proxmox with InfluxDB and Grafana in 4 Easy stepsMarch 1, 2022
Tried 12966 per your example, got error "failed to import dashboard."
Anonymous on Migrate existing Iptables to Nftables in RHEL8/CentOSFebruary 27, 2022
I followed the procedures and successfully loaded some weird 8081 port configurations needed for the app, however I discovered it…
sy on Install Ansible AWX on Kubernetes in 5 minutesFebruary 17, 2022
tried many times - followed all steps but was unable to setup custom context I always get -> The connection…
Faraz Ahmed on Prometheus with Grafana for Linux server monitoring in 5 easy stepsFebruary 7, 2022
Hello Babin Lonston, Your tutorial is very helpful to me to Install the prometheus and nodeexporter on the server. Can…