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iscsi centos

I've received a couple of email about setting up iSCSI under CentOS 4 or RHEL ES 4 server. Previously, I wrote about iSCSI under CentOS 5 / RHEL 5 server.

Requirements

[a] Following instructions tested on RHEL ES 4 and CentOS 4 only. (See RHEL 5/ CentOS 5 / Debian/ Ubuntu Linux specific instructions here).
[b] You need following information
[c] ISCSI Username
[d] ISCSI Password
[e] ISCSI Server IP / hostname

CentOS Linux v4.x - Install iscsi-initiator-utils

Type the following command:
# yum install iscsi-initiator-utils

Redhat ES Linux v4.x - Install iscsi-initiator-utils

Type the following command:
# up2date iscsi-initiator-utils

Configure iSCSI

Open /etc/iscsi.conf file, enter:
# vi /etc/iscsi.conf
Setup it as follows:

DiscoveryAddress=ISCSI_TARGET_HOST_OR_IP
 OutgoingUserName=ISCSI_USER_NAME
 OutgoingPassword=ISCSI_PASSWORD
 LoginTimeout=15

Save and close the file.

Start the iscsi service

Type the following command to start iscsi service so that you can see block device:
# chkconfig iscsi on
# /etc/init.d/iscsi start

Run any one of the following to find out new block device name:
# fdisk -l
# tail -f /var/log/messages
# find /sys/devices/platform/host* -name "block*"

Format iSCSI device

Use fdisk and mkfs.ext3 commands. First, create a partition (assuming that /dev/sdc is a new block device assigned to iscsi) :
# fdisk /dev/sdc
# mkfs.ext3 /dev/sdc1

Create /mnt/iscsi directory:
# mkdir -p /mnt/iscsi
Open /etc/fstab file and append config directive:
/dev/sdc1 /mnt/iscsi ext3 _netdev 0 0
Save and close the file. Mount the parition /dev/sdc1:
# mount -a
# df -H

Internet SCSI (iSCSI) is a network protocol s that allows you to use of the SCSI protocol over TCP/IP networks. It is good alternative to Fibre Channel-based SANs. You can easily manage, mount and format iSCSI Volume under Linux. It allows access to SAN storage over Ethernet.

Open-iSCSI Project

Open-iSCSI project is a high-performance, transport independent, multi-platform implementation of iSCSI. Open-iSCSI is partitioned into user and kernel parts.

Instructions are tested on:
[a] RHEL 5
[b] CentOS 5
[c] Fedora 7
[d] Debian / Ubuntu Linux

Install Required Package

iscsi-initiator-utils RPM package - The iscsi package provides the server daemon for the iSCSI protocol, as well as the utility programs used to manage it. iSCSI is a protocol for distributed disk access using SCSI commands sent over Internet Protocol networks. This package is available under Redhat Enterprise Linux / CentOS / Fedora Linux and can be installed using yum command:
# yum install iscsi-initiator-utils

A note about Debian / Ubuntu Linux

If you are using Debian / Ubuntu Linux install open-iscsi package, enter:
$ sudo apt-get install open-iscsi

iSCSI Configuration

There are three steps needed to set up a system to use iSCSI storage:

  1. iSCSI startup using the init script or manual startup. You need to edit and configure iSCSI via /etc/iscsi/iscsid.conf file
  2. Discover targets.
  3. Automate target logins for future system reboots.
  4. You also need to obtain iSCSI username, password and storage server IP address (target host)

Step # 1: Configure iSCSI

Open /etc/iscsi/iscsid.conf with vi text editor:
# vi /etc/iscsi/iscsid.conf
Setup username and password:
node.session.auth.username = My_ISCSI_USR_NAME
node.session.auth.password = MyPassword
discovery.sendtargets.auth.username = My_ISCSI_USR_NAME
discovery.sendtargets.auth.password = MyPassword

Where,

  • node.session.* is used to set a CHAP username and password for initiator authentication by the target(s).
  • discovery.sendtargets.* is used to set a discovery session CHAP username and password for the initiator authentication by the target(s)

You may also need to tweak and set other options. Refer to man page for more information. Now start the iscsi service:
# /etc/init.d/iscsi start

Step # 2: Discover targets

Now use iscsiadm command, which is a command-line tool allowing discovery and login to iSCSI targets, as well as access and management of the open-iscsi database. If your storage server IP address is 192.168.1.5, enter:
# iscsiadm -m discovery -t sendtargets -p 192.168.1.5
# /etc/init.d/iscsi restart

Now there should be a block device under /dev directory. To obtain new device name, type:
# fdisk -l
or
# tail -f /var/log/messages
Output:

Oct 10 12:42:20 ora9is2 kernel:   Vendor: EQLOGIC   Model: 100E-00           Rev: 3.2
Oct 10 12:42:20 ora9is2 kernel:   Type:   Direct-Access                      ANSI SCSI revision: 05
Oct 10 12:42:20 ora9is2 kernel: SCSI device sdd: 41963520 512-byte hdwr sectors (21485 MB)
Oct 10 12:42:20 ora9is2 kernel: sdd: Write Protect is off
Oct 10 12:42:20 ora9is2 kernel: SCSI device sdd: drive cache: write through
Oct 10 12:42:20 ora9is2 kernel: SCSI device sdd: 41963520 512-byte hdwr sectors (21485 MB)
Oct 10 12:42:20 ora9is2 kernel: sdd: Write Protect is off
Oct 10 12:42:20 ora9is2 kernel: SCSI device sdd: drive cache: write through
Oct 10 12:42:20 ora9is2 kernel:  sdd: unknown partition table
Oct 10 12:42:20 ora9is2 kernel: sd 3:0:0:0: Attached scsi disk sdd
Oct 10 12:42:20 ora9is2 kernel: sd 3:0:0:0: Attached scsi generic sg3 type 0
Oct 10 12:42:20 ora9is2 kernel: rtc: lost some interrupts at 2048Hz.
Oct 10 12:42:20 ora9is2 iscsid: connection0:0 is operational now

/dev/sdd is my new block device.

Step # 3: Format and Mount iSCSI Volume

You can now partition and create a filesystem on the target using usual fdisk and mkfs.ext3 commands:
# fdisk /dev/sdd
# mke2fs -j -m 0 -O dir_index /dev/sdd1

OR
# mkfs.ext3 /dev/sdd1

Tip: If your volume is large size like 1TB, run mkfs.ext3 in background using nohup:
# nohup mkfs.ext3 /dev/sdd1 &

Mount new partition:
# mkdir /mnt/iscsi
# mount /dev/sdd1 /mnt/iscsi

Step #4: Mount iSCSI drive automatically at boot time

First make sure iscsi service turned on at boot time:
# chkconfig iscsi on
Open /etc/fstab file and append config directive:
/dev/sdd1 /mnt/iscsi ext3 _netdev 0 0
Save and close the file.

Further readings: