====== iSCSI ======

**General Information**

iSCSI operations on Linux.

**Checklist**
  * Distro(s): Enterprise Linux 6/7

----

====== Adding Disks =====

  - Get the iscsi initiator name on the client<code bash>cat /etc/iscsi/initiatorname.iscsi</code>
  - Use the initiator name to configure the Host Group, LUN, and Host Affinity on your storage device. (Or send the initiator name to the storage admin)
  - From the client, discover the available LUNs on the storage device<code bash>iscsiadm --mode discovery -t sendtargets --portal <storage-ip-address></code>
  - Start and enable the iscsi daemon
    - EL6<code bash>service iscsid start
chkconfig iscsid on</code>
    - EL7<code bash>systemctl start iscsid
systemctl enable iscsid</code>
  - Log-in to the LUN with the iscsi client<code bash>iscsiadm --mode node --targetname <iqn-LUN#-here> --portal <storage-ip-address>:<port> --login</code>
  - Create /etc/multipath.conf if it doesn't exist<code bash>mpathconf --enable</code>
  - Configure multipath<code bash>vim /etc/multipath.conf
# Blacklist exception for your device
blacklist_exceptions {
    # WWN of LUN via iSCSI LUN group
    wwid "123456789"
}

# Setup your storage device specifics
devices {
      device {
              vendor "DELL"
              product "MODEL-HERE"
              # specify other options
      }
 }

# Setup the multipath
multipaths {
   multipath {
      wwid 123456789
      alias friendly_name_here
   }
}
</code>
  - Start and enable multipathd
    - EL6<code bash>service multipathd start
chkconfig multipathd on</code>
    - EL7<code bash>systemctl start multipathd
systemctl enable multipathd</code>
  - Re-scan the scsi bus<code bash>echo "- - -" > /sys/class/scsi_host/<host_number>/scan</code>
    - Where <host_number> is something like: host0 (there will probably be host0-3)
    - The hyphens represent controller,channel,lun, so – - – indicates all controllers, all channels, and all luns should be scanned.
  - Verify paths<code bash>multipath -ll</code>
  - Add mount entry to /etc/fstab
 

----

====== Clean Device Removal ======

Red Hat's recommended procedure for removing storage devices.

  - Ensure all files open on the device are closed<code bash>lsof | grep <devname></code>
  - Backup/move data as needed
  - Remove device from any software RAID or LVM volume
  - Remove device from multipath
  - Flush outstanding I/O (important for raw devices)<code bash>blockdev --flushbufs <device></code>
  - Remove references to the device from applications, scripts, etc.
  - Remove each path to the device from the SCSI subsystem<code bash>echo 1 > /sys/block/<device-name>/device/delete</code>
    - Where <device-name> can be something like 'sde'

----

====== iSCSI Admin ======

Example iscsiadm commands.

View iscsi target node IP addresses and target names
<code bash>
iscsiadm --mode node
</code>

Enable iscsi target: Login to iscsi target
<code bash>
iscsiadm --mode node --targetname <iscsi-target-name> --portal 192.168.1.100:3260 --login
</code>

Disable iscsi target: Logout from iscsi target
<code bash>
iscsiadm --mode node --targetname <iscsi-target-name> --portal 192.168.1.100:3260 --logout
</code>

Delete iscsi target
<code bash>
iscsiadm --mode node -o delete --targetname <iscsi-target-name> --portal 192.168.1.100:3260
</code>

----

===== Related Multipath Commands =====

If the iSCSI device that is removed is also multipath'd, remove it from multipath configuration also.

View multipath devices
<code bash>
multipath -ll
</code>

Remove (flush) an unused multipath device
<code bash>
multipath -F
</code>

After, restart multipathd to ensure it doesn't come back
  * EL6<code bash>service multipathd restart</code>
  * EL7<code bash>systemctl restart multipathd</code>

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