SAN w/o the cost – CentOS + iScsi

Nowadays, the iSCSI technology is quite popular in the storage world

Running iSCSI target on a Fedora system is as easy as “yum install iscsitarget” and configure the thing.

On CentOS – however  iSCSI Enterprise Target (IET) daemon is not in the default Yum repositories – and while CentOS does offer TGT  (Linux SCSI Target Framework) I think for a SAN – IET is best.

In short – this requires us to start from scratch – and build from source.  It is important to note – whenever you update your kernel – you will need to recompile.

The iSCSI Target system

First, some prerequisites :

# yum install openssl-devel kernel-dev gcc rpm-build

Download the latest IET from the Sourceforge repo and put the tgz in /usr/src

# cd /usr/src
# tar xvf iscsitarget-0.4.17.tar.gz
# cd iscsitarget-0.4.17
# make
# make install

Like most everything in linux – now that the make install is complete – your ready to go (except a minor configuration of course).  The iscsi-target init.d script is installed and will be started at boot-time.

Configuring the ietd host is pretty simple and the WIKI has tons of valuable information.
First, lets decide who can connect to the IET daemon :

First you have to have a naming convention for your IQN (iScsi Qualified Name) -   The IQN is an identifier for your iSCSI target.

Ok – so glenn – what the heck is this needed for? – I’m glad you asked..   The iSCSI initiator using the IQN to connect to the disks/lun’s.

# nano /etc/initiators.allow

iqn.namingconvension:mydiskname 10.0.100.0/24

In the above example The subnet 10.0.100.0/24 is allowed to use this iSCSI target.

Next, we’ll create the initiators.deny file, which is pretty straightforward :

 # nano /etc/initiators.deny

ALL:ALL

Time to create the IQN in the ietd configuration file.

# nano /etc/ietd.conf

Target
iqn.namingconvension:mydiskname
IncomingUser username 12345
OutgoingUser username 123456789012
Lun 0 Path=/dev/SAN/diskname,Type=fileio,IOMode=wb
Alias iSCSI for diskname
ImmediateData Yes
MaxConnections 1
InitialR2T Yes

I use the following conventions, as defined in the RFC :

For IncomingUser: Password always 5 characters
For OutgoingUser: Password always 12 characters

I suggest using LVM as a disk backend. The disk can also be /dev/sdb or whatever your heart desires…

The iSCSI Initiator

In Ubuntu/Debian/Fedora/ (or pick your Nix version and place here) there usually is an open-iscsi in the repository. If not, you can always compile it from source at http://www.open-iscsi.org.

I love the CentOS Nix version – so the directions below – are assuming you have a CentOS system you would like to use with your new san.

Let’s install the prerequisites :

# yum install iscsi-initiator-utils
# yum install open-iscsi

Next, define the initiator name. This is in the exact same form as the target name, but it should not be the same. This initiator name is the name (in IQN) of your computer.

# nano /etc/iscsi/initiatorname.iscsi

InitiatorName=iqn.namingconvension:someuniquename

Next, we’re going to configure the authentication and some specials in the iscsid config.

# nano /etc/iscsi/iscsid.conf

node.startup = automatic
node.session.auth.authmethod = CHAP
node.session.auth.username = username
node.session.auth.password = 12345
node.session.auth.username_in = username
node.session.auth.password_in = 123456789012
node.session.timeo.replacement_timeout = 120
node.conn[0].timeo.login_timeout = 15
node.conn[0].timeo.logout_timeout = 15
node.conn[0].timeo.noop_out_interval = 10
node.conn[0].timeo.noop_out_timeout = 15
node.session.initial_login_retry_max = 10
node.session.cmds_max = 128
node.session.queue_depth = 32
node.session.iscsi.InitialR2T = No
node.session.iscsi.ImmediateData = Yes
node.session.iscsi.FirstBurstLength = 262144
node.session.iscsi.MaxBurstLength = 16776192
node.conn[0].iscsi.MaxRecvDataSegmentLength = 131072
discovery.sendtargets.iscsi.MaxRecvDataSegmentLength = 32768
node.session.iscsi.FastAbort = No

For more information about these setting, please refer to the open-iscsi page.
Next up, start the thing :

# service iscsi start

Bingo! You just started the iSCSI daemon (all cheer).

Now, we’re going to discover our targets on the target iSCSI host. I assume 10.0.100.1 is the target host in this example.

# iscsiadm -m discovery -t st -p 10.0.100.1
10.0.100.1:3260,1 iqn.namingconvension:mydiskname

As you can see, it found the target we created before. Now, let’s login to it:

# iscsiadm -m node -p 10.0.100.1  -T iqn.namingconvension:mydiskname --login

Congratulations Chap – if you do dh -alh – or dmesg  you will find a new disk inserted (/dev/sdc or whatever).