iSCSI Server and client in CentOS 7

iSCSI (internet Small Computer System Interface) is common way to export storage to a client in enterprise environments (e.g. Clustering with DRBD). In this example, I'll show how to install the iscsi-server and map the exportet LUN to the client.

I'm assuming you have a clean and updated version of CentOS 7.3 installed both on client the client and the server.

My server's ip: 172.31.10.34
My client's ip: 172.31.10.35

We'll start by configuring the server.

First we have to install the package 'targetcli'. This utility is used for all the configuration done.

 [archy@storage01 ~]$ sudo yum -y install targetcli

Enable the service to start on boot and start it now.

 [archy@storage01 ~]$ sudo systemctl enable target.service && sudo systemctl start target.service

Start the configuration by running

 [archy@storage01 ~]$ sudo targetcli

Before configuring the iSCSI-Target I want to mention that there are two options to allocate the storage. The first options is 'blockio' which means that it exports a device (e.g. /dev/vg/lvm_volume1).
The other option is 'fileio' which means that we are going to export a storage file (e.g. /storage/iscsi.img).

I'll be configuring a target using fileio.

 targetcli> backstores/fileio/ create iscsi-lun0 /storage/iscsi-lun0 300M

This creates a 300MB unallocated file with the path '/storage/iscsi-lun0'.

Before exporting, we need to assign a iqn (iSCSI Qualified Name) to the host and add a target portal group. Format needs to be iqn:tpg.

 targetcli> iscsi/ create iqn.2017-08.lan.archyslife:iscsi-lun0  
 targetcli> cd iscsi/iqn.2017-08.lan.archyslife:iscsi-lun0/tpg1

From here we can add / edit / delete the acls and portals.

So first we create our initial LUN.

 targetcli> luns/ create /backstores/fileio/iscsi-lun0

Now create an acl for our client allowing it to map the iscsi-lun.

 targetcli> acls/ create iqn.2017-08.lan.archyslife:client

There is also the option to add a username and password to the lun by running

 targetcli> acls/iqn.2017-08.lan.archyslife:client/ set auth userid=archy  
 targetcli> acls/iqn.2017-08.lan.archyslife:client/ set auth password=your_secret_password

Now since CentOS 7.1 there is usually a standard portal set pointing to '0.0.0.0:3260'. I prefer to delete that one and create my own. I'm using the IP-Address of my client (172.31.10.35). along with the standard iSCSI-Port (3260).

 targetcli> portals/ create ip_address=172.31.10.35 ip_port=3260  
 targetcli> exit

Add the iSCSI-Port to the firewall settings and make them persistent.

 [archy@storage01 ~]$ sudo firewall-cmd --zone=internal --add-service=3260/tcp --permanent  
 [archy@storage01 ~]$ sudo firewall-cmd --reload

That concludes the server's setup.

The client is quite simple. First install the iscsi-initiator

 [archy@client ~]$ sudo yum -y install iscsi-initator-utils

Next, edit the file /etc/iscsi/initatorname.iscsi and replace the standard value with the initatorname you set in your lun-acl above.

 InitiatorName=iqn.2017-08.lan.archyslife:client

If you have setup user and password in the config for your lun, you'll have to enter these in the
/etc/iscsi/iscsid.conf. Edit the following lines

 node.session.auth.authmethod = CHAP  
 node.session.auth.username = archy  
 node.session.auth.password = your_secret_password

Save and edit. Now start the iscsi.service (not iscsid.service)

 [archy@client ~]$ sudo systemctl start iscsi

Run iscsiadm to discover and login to your discovered target.

 [archy@client ~]$ sudo iscsiadm --mode discovery --type sendtargets --portal 172.31.10.34

Now that the target was discovered, you can login to it by executing

 [archy@client ~]$ sudo iscsiadm --mode node --targetname iqn.2017-08.lan.archyslife:iscsi-lun0 --portal 172.31.10.34 --login

Your iSCSI-LUN is now mounted to your machine, but there is no filesystem on it whatsoever.
We will first get the iSCSI's devicename by running

 [archy@client ~]$ lsblk --scsi

The disk with it says your lun on the model is the target. In my case it is /dev/sdb.
Make the filesystem on it and mounting it can be done the ususal way.

 [archy@client ~]$ sudo mkfs.xfs /dev/sdb  
 [archy@client ~]$ sudo mount /dev/sdb /mnt

That completes the iSCSI-Target and Initiator setup.

Feel free to comment and / or suggest a topic.

Comments

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