Internet SCSI (iSCSI) is a network protocol that allows you to use of the SCSI protocol over TCP/IP networks. It’s good alternative to Fibre Channel-based SANs. You can easily manage, mount and format iSCSI volumes under Linux.

Definitions: the iSCSI Target is the server that hosts and exports volumes to the clients. The iSCSI Initiator is the client that use the configured volumes.

On the server you need to install this package, start the related service and ensure that it starts on boot:

# yum -y install scsi-target-utils

# service tgtd start

# chkconfig tgtd on

On the client side you need to install this package, start the related service and ensure that it starts on boot:

# yum -y install iscsi-initiator-utils

# service iscsid start

# chkconfig iscsid on

Now configure your LUNs on the target:

# vim /etc/tgt/targets.conf

This is a basic configuration for target:

<target iqn.yyyy-mm.reverse-hostname:label>

# use backing-store to export a specific volume…

backing-store /dev/vol_group_name/logical_volume_name

# …or use direct-store to export the entire device

# direct-store /dev/sdb

</target>

Don’t forget to restart the tgtd service after a configuration update:

# service tgtd restart

Now it’s time to check if your LUNs are being exported correctly. The next command will show two LUNs for each target. The first one (LUN 0) is the controller, the second one (LUN 1) is your volume. Run this command on the target:

# tgtadm –lld iscsi –op show –mode target

Remember to enable iSCSI ports on iptables in order to accept connection on port 3260 for both TCP and UDP protocols!

Ok, your target is now fully configured. You can logon on your client and start to use the remote storage. On the client run these commands to show the exported volumes and login to them:

iscsiadm -m discovery -t sendtargets -p target_ipaddress

iscsiadm -m node -T target_name_iqn -p target_ipaddress –login

Now restart the iscsid service, use fdisk to show the mounted device on /dev and create partitions on it.

If you need to detach from the target you have to logout from it:

iscsiadm -m node -T target_name_iqn -p target_ipaddress –logout