How to setup iSCSI on Linux (RedHat)

Definitions:

iSCSI initiator : the endpoint that initiates a iSCSI session.  An iSCSI initiator sends SCSI commands over an IP network. It’s the client endpoint.

iSCSI Target : refers to a storage resource located on an iSCSI server (most of the time it’s a “storage array”). It’s the server endpoint.

LUNs (Logical Number Units): number used to identify a logical unit, which is a device addressed by the SCSI protocol (thus Fiber Channel or iSCSI). It usually represents slices of large RAID disk arrays.

IQN (iSCSI Qualified Name) : iSCSI name of the target or initiator.

On the Storage Server:

Enable and configure the iSCSI Target on your storage server.

Mine is a QNAP Turbo NAS. I’ve got 1 target with 5 LUNs configured.

SCSI Portal
 
X Enable iSCSI Target Service
 
iSCSI Service Port:           3260
 
mytarget (iqn.2004-04.com.qnap:ts-859:iscsi.mytarget.c5884b)     Connected
 
id:0 - lun1 ( 2024.00 GB)               Enabled
 
id:1 - lun2 ( 2024.00 GB)               Enabled
 
id:2 - lun3 ( 2024.00 GB)               Enabled
 
id:3 - lun4 ( 2024.00 GB)               Enabled
 
id:4 - lun5 ( 1804.13 GB)               Enabled

I have two network interfaces:

1-       for QNAP management, IP : 10.0.0.5

2-      iSCSI access, directly connected to the server : 192.168.0.1

For more security you can enable “LUN masking”. It will restrain iSCSI target to be accessed to only by the initiator of your client (the client initiator name IQN can be found on /etc/iscsi/initiatorname.iscsi).

On the Linux client (see tips ** for VMware configuration) :

Install “iscsi-initiator-utils” on the server that will connect to the iSCSI volume:

# rpm –Uvh iscsi-initiator-utils-6.2.0.865-6.el5.x86_64.rpm

Set up iscsi automatic start on boot and start iscsi services:

# chkconfig iscsid on
# service iscsid start
# chkconfig iscsi on
# service iscsi start

Discover your iSCSI targets:

# iscsiadm -m discovery -t st -p 192.168.0.1

In my case it will show 2 targets (one for each network connection):

192.168.0.1:3260 iqn.2004-04.com.qnap:ts-859:iscsi. mytarget.c5884b
10.0.0.5:3260 iqn.2004-04.com.qnap:ts-859:iscsi. mytarget.c5884b

I have 2 routes for the same target.

Log to the target through IP 192.168.0.1 :

# iscsiadm -m node -T iqn.2004-04.com.qnap:ts-859:iscsi.mytarget.c5884b -p 192.168.0.1 -l

Add automatic login at boot :

# iscsiadm -m node -T iqn.2004-04.com.qnap:ts-859:iscsi.mytarget.c5884b -p 192.168.0.1 --op update -n node.startup -v automatic

As I have another access to the target, I will disable it in order to not disturb the previous configuration:

# iscsiadm -m node -T iqn.2004-04.com.qnap:ts-859:iscsi.mytarget.c5884b -p 10.0.0.5 --logout
# iscsiadm -m node -T iqn.2004-04.com.qnap:ts-859:iscsi.mytarget.c5884b -p 10.0.0.5 --op update -n node.startup -v manual

At this point you will see the iSCSI LUNs as block devices on your client.

On my system the five iSCSI block devices are /dev/sdc, sdd, sde, sdf and sdg.

You will have create partitions and format them to either standard Linux partition or LVM partition.

I chose LVM because I need large file systems.

You can use parted or fdisk (if < 2To), see article: ” How To Make Partitions Larger Than 2To With Parted GPT Support“.

So here is the result:

# fdisk -l
Disk /dev/sdc: 2173.2 GB, 2173253451776 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/sdc1               1      264216  2122314988+  8e  Linux LVM
Disk /dev/sdd: 2173.2 GB, 2173253451776 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/sdd1               1      264216  2122314988+  8e  Linux LVM
Disk /dev/sde: 2173.2 GB, 2173253451776 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/sde1               1      264216  2122314988+  8e  Linux LVM
Disk /dev/sdf: 2173.2 GB, 2173253451776 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/sdf1               1      264216  2122314988+  8e  Linux LVM
Disk /dev/sdg: 1937.1 GB, 1937169711104 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/sdg1               1      235514  1891766173+  8e  Linux LVM

Then create you LVM volume group and logical volume :

# pvcreate /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1
# vgcreate -s 256M vol_vg /dev/sdc1 /dev/sdd1 /dev/sde1 /dev/sdf1 /dev/sdg1
# lvcreate -l 28672 vol_vg -n vol_lv1
# lvcreate -l 10924 vol_vg -n vol_lv2

File system creation:

# mkfs -t ext3 -b 4096 -N 100000 /dev/vol_vg/vol_lv1 -L VOL1
# mkfs -t ext3 -b 4096 -N 100000 /dev/vol_vg/vol_lv2 -L VOL2

Then mount the file systems:

# mkdir –p /VOL1 /VOL2
# mount -t ext3 /dev/vol_vg/vol_lv1 /VOL1
# mount -t ext3 /dev/vol_vg/vol_lv2 /VOL2
# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/vol_vg-vol_lv1 7.0T  6.3T  395G  95% /VOL1
/dev/mapper/vol_vg-vol_lv2 2.7T  1.5T  1.2T  57% /VOL2

If you will want to automatically mount your iSCSI file systems at startup (see article: How To Use UUID And Blkid To Manage Devices).

Get the UUID for each file system:

# blkid /dev/vol_vg/vol_lv1
/dev/vol_vg/vol_lv1: LABEL="VOL1" UUID="4a496f92-6840-4736-a0d5-5b9916113835" SEC_TYPE="ext2" TYPE="ext3"
# blkid /dev/vol_vg/vol_lv2
/dev/vol_vg/vol_lv2: LABEL="VOL2" UUID="cab5e3ec-4797-4227-98e8-e9bca3c3f766" SEC_TYPE="ext2" TYPE="ext3"

The add UUIDs to /etc/fstab :

UUID=4a496f92-6840-4736-a0d5-5b9916113835       /VOL1   ext3 _netdev    0 0
UUID=cab5e3ec-4797-4227-98e8-e9bca3c3f766       /VOL2   ext3 _netdev    0 0

** Tip :

If your Linux is a VM on ESXi :

–          Dedicate a network adapter to connect directly the Storage Array to the VMware server.

CAT 5e/6 RJ45 cable (through dedicated hardware switch, if needed).

–          Create a “vSwitch” using the dedicated network adapter with vShere Client.

vswitch iscsi

–          Add a network adapter using the new vSwitch on your virtual host configuration.

Now you have a direct iSCSI connection to you storage array. You can start the configuration.