iSCSI Initiator for Linux

Prerequisite:

Package iscsi-initiator-utils
Package device-mapper-multipath

Installing:

Install the iSCSI initiator and multipath tools:

yum install iscsi-initiator-utils
yum install device-mapper-multipath

Configuring:

Create the default /etc/multipath.conf file and enable the multipathd service:
```
mpathconf --enable --with_multipathd y
```

Add the following to the /etc/multipath.conf file:

devices {
        device {
                vendor                 "LIO-ORG"
                product                "TCMU device"
                hardware_handler       "1 alua"
                path_grouping_policy   "failover"
                path_selector          "queue-length 0"
                failback               60
                path_checker           tur
                prio                   alua
                prio_args              exclusive_pref_bit
                fast_io_fail_tmo       25
                no_path_retry          queue
        }
}

Restart the multipathd service:
```
systemctl reload multipathd
```

iSCSI Discovery and Setup:

Enable CHAP authentication and provide the initiator CHAP username and password by uncommenting and setting the following options in the /etc/iscsi/iscsid.conf file:
```
node.session.auth.authmethod = CHAP
node.session.auth.username = myusername
node.session.auth.password = mypassword
```
If you intend to use mutual (bidirectional) authentication, provide the target CHAP username and password:
```
node.session.auth.username_in = mytgtusername
node.session.auth.password_in = mytgtpassword
```

Discover the target portals:

iscsiadm -m discovery -t st -p 192.168.56.101

192.168.56.101:3260,1 iqn.2003-01.org.linux-iscsi.rheln1
192.168.56.102:3260,2 iqn.2003-01.org.linux-iscsi.rheln1

Log in to the target:

iscsiadm -m node -T iqn.2003-01.org.linux-iscsi.rheln1 -l

Multipath IO Setup:

The multipath daemon (multipathd) uses the multipath.conf settings to set up devices automatically. Running the multipath command shows that the devices have been set up in a failover configuration. Notice that each path has been placed into its own priority group:
```
multipath -ll
```
```
mpathbt (360014059ca317516a69465c883a29603) dm-1 LIO-ORG ,IBLOCK
size=1.0G features='0' hwhandler='1 alua' wp=rw
|-+- policy='queue-length 0' prio=50 status=active
| `- 28:0:0:1 sde  8:64  active ready running
`-+- policy='queue-length 0' prio=10 status=enabled
  `- 29:0:0:1 sdc  8:32  active ready running
```
You should now be able to use the RBD image in the same way that you would use a normal multipath iSCSI disk.

Log out of the target:

iscsiadm -m node -T iqn.2003-01.org.linux-iscsi.rheln1 -u