Setting Up ISCSI Target & Initiator

ISCSI stands for  Internet Small Computer Systems Interface, which is an IP-based storage,and works on top of internet protocol by carrying SCSI commands over IP network. iSCSI transports block-level data between an iSCSI initiator(on the Client machine) and an iSCSI target on a storage device (server).

Before getting into the Configuration of an iscsi target and initiator, let’s talk a little bit about iscsi Terminology as your acquaintance with the definitions will light up the path for you to understand the subject profoundly.

Iscsi Terminology
iscsi Target: you already know about iscsi target , it is actually the server that share the block device and to which you log in . the disk is configured as an iscsi target through targetcli utility and becomes available to the clients.
iscsi Initiator: the shared device is requested with initiator which resides on the client , the initiator itself is installed through iscsi-initiator-utils on the client machine.

IQN(WWN):Internet Qualified Name or World Wide Name is a unique name with which the initiator’s privilege and identity is recognized.

ACL: an Access Control List which is based on node iqn.

LUN: Logical Unit which is the block device that is shared through target.

TPG: Target Portal Group, the collection of IP Addresses to which a specific iscsi target listens.

Environment

Now let’s get into work , we should have 2 centos 7 machines as bellow

Server: kserver.lab

IP Address: 192.168.1.200

Client: client.kserver

IP Address: 192.168.1.201

Preparing an LVM Partition on the target

Before starting the configuration we should prepare a new disk to be shared , I intend to prepare the disk with lvm(Logical Volume Manager) , because the best practice is that , on the target you will be able to extend or shrink the partitions easily .
I have added a new disk /dev/sdc and I am going to make an lvm partirion using fdisk utility.

Let’s approach it step by step :)

#1-making sure that the disk is recognized by the system
#cat /proc/partitions

As you can see the new disk is recognized by the system.
#2-Use fdisk to create the partition

#fdisk /dev/sdc

At this point type m for help to see options that are available for creating the partition.

For creating a new partition we must press n

Target Configuration

We are going to configure backend device for sharing , first we need to install targetcli package .
# yum install targetcli

The targetcli is a command line interface through which you are capable of creating block backend device as well as creating Logical Units(LUNs) and Access Control Lists(ACL).based on the man pages targetcli is a shell for viewing, editing, and saving the configuration of the kernel's target subsystem, also known as LIO. It enables the administrator to assign local storage resources backed by either files, volumes, local SCSI devices, or ramdisk, and export them to remote systems via network fabrics, such as iSCSI or FCoE. once the installation is done you can easily type targetcli to jump into it’s interface and this is what you will encounter.

Targetcli is an intuitive utility, although it is not obvious from the beginning. you can see in the picture that it starts with a prompt and there is also a help command provided, and if you type ls you can see my previous configuration will appear, but since, I am intending to create a fresh configuration, let’s clear the Current one.

In targetcli prompt type the following command to clear the existing configuration

/> clearconfig confirm=true

So we have a cleared configuration at the moment, let’s start exploring the items of the above figure. the first item to address is backstores, which are different kinds of local storage resources that the kernel target uses to "back" the SCSI devices it exports. The mappings to local storage resources that each backstore creates are called storage objects, and since we are going to share a disk partition we should create a block object .
/>cd backstores

/backstores > block / create dev=/dev/sdc name=sdc

We specify that we are going to create a block device with the name sdc on /dev/sdc and in this way our disk backend is prepared the next step is to create an iscsi to share .

/backstores>cd ../iscsi

/iscsi> create wwn=iqn.2018-02.lab.kserver:disk

The format for wwn should be iqn.<year>-<month>.<Reverse DNS>:<an Optional Name>

After Creating the iscsi device the result of ls would be

/iscsi> cd iqn.2018-02.lab.kserver:disk/tpg1/luns

/iscsi/iqn.20...isk/tpg1/luns> create /backstores/block/sdb

Now we have created a lun on the block device and the next step is to create access control list.in the picture you see that the target is going to listen on port 3260 on all incoming connections, with acl we define the allowed initiator to connect.the next step is setting up acl but first, we should setup initiator to be able to get the iqn for the acl , let’s continue on the second machine and run the following command :
[root@client ~] #yum install iscsi-initiator-utils

This will install a set of utilities to connect to the target , now let’s get the iqn of the initiator by running the following command:

[root@client ~]# cat /etc/iscsi/initiatorname.iscsi

InitiatorName=iqn.1994-05.com.redhat:26bdc0c78251

So now we have the iqn of the initiator let’s get back to the target and run create acl for the initiator 

/iscsi/iqn.20...isk/tpg1/luns> cd ../acls

create wwn=iqn.1994-05.com.redhat:26bdc0c78251

now we are done , let’s run cd / to get to the root of our configuration and the run ls:

Wonderful!, isn’t it?

Now let’s get back to the initiator and do some connectivity test .but first we need to add iscsi-target service to firewall . just commit the following command on the target.

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

iscsiadm (open-iscsi administration utility) is part of iscsi-initiator-utils package. it has fantastic option for connecting to iscsi target.

# iscsiadm --mode discoverydb --type sendtargets --portal 192.168.1.200 --discover

this command would discover the target shared device and if everything has been set up correctly, it will return following message as output.

192.168.1.200:3260,1 iqn.2018-02.lab.kserver:disk

now that we are connected , we can  login to the target .
# iscsiadm --mode node --targetname iqn.2018-02.lab.kserver:disk --portal 192.168.1.200:3260 --login

Mounting and using the Shared Device

now we are going to configure the Initiator to mount and use the shared block device, In order to do so, we must make a fileSystem on top of an LVM Disk , let’s first see what do we have !
commit the following command to see what SCSI devices are available:

#lsscsi

[1:0:0:0]    cd/dvd  VBOX     CD-ROM           1.0   /dev/sr0

[2:0:0:0]    disk    ATA      VBOX HARDDISK    1.0   /dev/sda

[3:0:0:0]    disk    LIO-ORG  sdc              4.0   /dev/sdb

The result shows that /dev/sdb is with the name of sdc is currently available as scsi Device. the next step is to create a physical volume , let’s do it

#pvcreate /dev/sdb

Now we must create a volume group so that our physical volume can be added to the volume group we name the volume Group vgsan:

#vgcreate vgsan /dev/sdb1

After creating the Volume Group comes Logical Volume and we name our Logical Volume lvsan:

#lvcreate -l 100%FREE -n lvsan vgsan

Now, All we have to do is to make a file system and put a mount point and add an entry to the file /etc/fstab:

#mkfs.ext4 /dev/vgsan/lvsan

#mkdir /san

/san directory is our mount point and to make mounting of the new partition persistent, we shall add an entry to /etc/fstab:

#nano /etc/fstab

Add following line

/dev/vgsan/lvsan            /san                ext4    _netdev         0 0

#mount -a

#reboot

And if your configuration on the target survives a reboot it you will have fully operational iscsi device shared and mounted and ready to be used.