Linux iSCSI Targets and Initiators (2025)

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This article provides an overview of configuring iSCSI targets and initiators on Linux, with specific reference to the information needed for the RHCE EX300 certification exam.

Remember, the exams are hands-on, so it doesn't matter which method you use to achieve the result, so long as the end product is correct.

• iSCSI Targets
• iSCSI Initiators

Related articles.

• Linux Disk Partitioning (fdisk, parted)
• Linux File Systems (mkfs, mount, fstab)

iSCSI Targets

Configuration of iSCSI targets is not part of the exam, but you are going to need some to test the iSCSI intiator configuration.

Install the necessary package to support the creation of iSCSI targets.

# yum install scsi-target-utils

Turn on the service and make sure it starts automatically after reboot.

# service tgtd start# chkconfig tgtd on

I have a virtual machine called "rhce2.localdomain" with an additional virtual hard drive called "/dev/sdb". If you want to make permanent iSCSI targets, you need to add modify the "/etc/tgt/targets.conf" file. The following entry will create an iSCSI target for this disk device.

<target rhce2:drive1> backing-store /dev/sdb</target>

After amending the "/etc/tgt/targets.conf" file you need to restart the tgtd service.

# service tgtd restart

The target will now be visible using the following command.

# tgtadm --lld iscsi --mode target --op showTarget 1: rhce2:drive1 System information: Driver: iscsi State: ready I_T nexus information: LUN information: LUN: 0 Type: controller SCSI ID: IET 00010000 SCSI SN: beaf10 Size: 0 MB, Block size: 1 Online: Yes Removable media: No Prevent removal: No Readonly: No Backing store type: null Backing store path: None Backing store flags: LUN: 1 Type: disk SCSI ID: IET 00010001 SCSI SN: beaf11 Size: 12885 MB, Block size: 512 Online: Yes Removable media: No Prevent removal: No Readonly: No Backing store type: rdwr Backing store path: /dev/sdb Backing store flags: Account information: ACL information: ALL#

If you are using the Linux firewall you will need to make sure the TCP port 3260 is open on the server. Assuming you are using a firewall setup file, as described here, you can include the following addition to the INPUT chain.

# Open port for iSCSI.iptables -A INPUT -p udp --dport 3260 -j ACCEPT

This is the simplest way to create iSCSI targets. Some resources suggest you use the tgtadm command. The example below describes how that works, but it is quite long-winded in comparison to amending the "/etc/tgt/targets.conf" file and the targets are not permanent.

The man page for the tgtadm command includes examples of creating an iSCSI target. The example in the man page looks like this.

# Create a targettgtadm --lld iscsi --mode target --op new --tid 1 --targetname iqn.2007-03:virtual-dvd:‘hostname‘

I have a virtual machine called "rhce2.localdomain" with an additional virtual hard drive called "/dev/sdb". First we must create and empty target.

# tgtadm --lld iscsi --mode target --op new --tid 1 --targetname rhce2:drive1

Add a LUN to this target.

# tgtadm --lld iscsi --mode logicalunit --op new --tid=1 --lun=1 --device-type disk --backing-store=/dev/sdb

Allow the target to accept intitiators.

# tgtadm --lld iscsi --mode target --op bind --tid=1 --initiator-address=ALL

Show the iSCSI targets that are available.

# tgtadm --lld iscsi --mode target --op showTarget 1: rhce2:drive1 System information: Driver: iscsi State: ready I_T nexus information: LUN information: LUN: 0 Type: controller SCSI ID: IET 00010000 SCSI SN: beaf10 Size: 0 MB, Block size: 1 Online: Yes Removable media: No Prevent removal: No Readonly: No Backing store type: null Backing store path: None Backing store flags: LUN: 1 Type: disk SCSI ID: IET 00010001 SCSI SN: beaf11 Size: 12885 MB, Block size: 512 Online: Yes Removable media: No Prevent removal: No Readonly: No Backing store type: rdwr Backing store path: /dev/sdb Backing store flags: Account information: ACL information: ALL#

iSCSI Initiators

This section is the only part of the article that is actually relevant for the RHCE EX300 certification exam.

Install the necessary software to support iSCSI initiators.

# yum install iscsi-initiator-utils

Turn on the service and make sure it starts automatically after a reboot.

# service iscsi start# chkconfig iscsi on

Check for iSCSI targets on the server presenting them. I configured the target on a machine called "rhce2.localdomain".

# iscsiadm --mode discoverydb --type sendtargets --portal rhce2.localdomain:3260 --discoverStarting iscsid: [ OK ]192.168.0.191:3260,1 rhce2:drive1#

Restart the iSCSI service.

# service iscsi restartStopping iscsi: [ OK ]Starting iscsi: [ OK ]#

The iSCSI device is now visible using the fdisk -l command.

# fdisk -lDisk /dev/sda: 21.5 GB, 21474836480 bytes255 heads, 63 sectors/track, 2610 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisk identifier: 0x000819e0 Device Boot Start End Blocks Id System/dev/sda1 * 1 64 512000 83 LinuxPartition 1 does not end on cylinder boundary./dev/sda2 64 2611 20458496 8e Linux LVMDisk /dev/mapper/vg_rhce1-lv_root: 18.8 GB, 18832424960 bytes255 heads, 63 sectors/track, 2289 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisk identifier: 0x00000000Disk /dev/mapper/vg_rhce1-lv_swap: 2113 MB, 2113929216 bytes255 heads, 63 sectors/track, 257 cylindersUnits = cylinders of 16065 * 512 = 8225280 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisk identifier: 0x00000000Disk /dev/sdb: 12.9 GB, 12884901888 bytes64 heads, 32 sectors/track, 12288 cylindersUnits = cylinders of 2048 * 512 = 1048576 bytesSector size (logical/physical): 512 bytes / 512 bytesI/O size (minimum/optimal): 512 bytes / 512 bytesDisk identifier: 0x00000000#

Partition it and build a filesystem on it, as shown here and here. In this case I used the following commands.

# fdisk /dev/sdb# mkfs.ext4 /dev/sdb1

Check the UUID of the new partition.

# blkid /dev/sdb1/dev/sdb1: UUID="eac38663-e202-4920-b046-93b798db18b1" TYPE="ext4"#

This UUID should be used for mounting the device, thus preventing problems if device names change. Create a new mount point.

# mkdir /rhce2_drive1

Add the following entry into the "/etc/fstab" file.

UUID="eac38663-e202-4920-b046-93b798db18b1" /rhce2_drive1 ext4 defaults 0 0

Mount the device.

# mount /rhce2_drive1

The drive is now mounted and will be available on reboot.

For more information see:

• RHEL6 Storage Administration Guide
• tgtadm man page
• iscsiadm man page
• Linux man pages
• RHCSA and RHCE
• Linux Disk Partitioning (fdisk, parted)
• Linux File Systems (mkfs, mount, fstab)

Hope this helps. Regards Tim...

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