ISCSI

Introduction

iSCSI (internet SCSI) is an application layer protocol that enables the transport of SCSI commands over a TCP/IP network.

This documentation was created on Red Hat 5 and is compatible with Red Hat 6.

Server

Installation

To install an iSCSI server:

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yum install scsi-target-utils

Creating partitions

Create your partitions, then have them detected with a command like:

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partx -a /dev/sda

or

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partprobe /dev/sda

Preferably use partx.

Note: For the following steps, I strongly recommend using UUIDs instead of device paths (/dev/xxx). In this documentation, device paths are used for simplicity.

Configuration

Let’s edit the server configuration file and uncomment the “target” section:

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<target iqn.2012-02.fr.deimos.www:iscsi>
        # List of files to export as LUNs
        #backing-store /usr/storage/disk_1.img
        backing-store /dev/sda1
        # Authentication:
        # if no "incominguser" is specified, it is not used
        #incominguser backup secretpass12

        # Access control:
        # defaults to ALL if no "initiator-address" is specified
        #initiator-address 192.168.1.2
        initiator-address 192.168.0.1
</target>
  • Here’s how to name the iSCSI target, which must be unique: ign..<reverse_dns>.[:]
    • date: year + month (yyyy-mm)
    • reverse_dns: reversed DNS (fr.deimos.www)
    • strings: name to identify this device (myiscsi)
    • :: optional, allows adding a name
  • backing-store: the disk device or disk image to use
  • initiator-address: client addresses authorized to mount this device

Start the service and make it persistent:

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chkconfig tgtd on
service tgtd start

Check the configuration like this:

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> tgt-admin -s
Target 1: iqn.2012-02.fr.deimos.www:iscsi
    System information:
        Driver: iscsi
        State: ready
    I_T nexus information:
    LUN information:
        LUN: 0
            Type: controller
            SCSI ID: deadbeaf1:0
            SCSI SN: beaf10
            Size: 0 MB
            Online: Yes
            Removable media: No
            Backing store: No backing store
        LUN: 1
            Type: disk
            SCSI ID: deadbeaf1:1
            SCSI SN: beaf11
            Size: 5369 MB
            Online: Yes
            Removable media: No
            Backing store: /dev/sda1
    Account information:
    ACL information:
        192.168.0.1

Here’s how to get information about iSCSI devices:

  • /sys/class/scsi_host: all detected iSCSI adapters
  • /sys/block: lists the peripherals

Client

Installation

Clients are called “Initiators” and the target is the recipient (disk array/server). To install the client:

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yum install iscsi-initiator-utils

Then we’ll start the service:

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chkconfig iscsi on
service iscsi start

Usage

Mounting

First, let’s perform a “discovery” to see what devices are available to us:

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> iscsiadm --mode discoverydb --type sendtargets --portal <server> --discover
iqn.2012-02.fr.deimos.www:iscsi
  • <server>: enter the IP address of the server (not DNS!!!)

Then we’ll log in to the device so that it will be mounted on each reboot:

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iscsiadm --mode node --targetname <iqn.2012-02.fr.deimos.www:iscsi> --portal 192.168.1.1:3260 --login
  • iqn.2012-02.fr.deimos.www:iscsi: the IQN of the server to use
  • <server>: enter the IP address of the server (not DNS!!!)

Once logged in, you can retrieve device information from the logs:

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tail -20 /var/log/messages | grep "/dev"

If you need more information, use verbose mode:

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iscsiadm -m node -P 1

Next, format the partition in the desired format. Add a line to fstab with the “_netdev” option, otherwise the machine won’t be able to reboot because of the rc.sysinit script. This specifies that the device doesn’t use networking:

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/dev/sda1 /mnt/iscsi  ext3   defaults,auto,_netdev 0 0

Unmounting

To temporarily unmount an iSCSI device (until the next reboot):

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iscsiadm -m node -T <iqn.2012-02.fr.deimos.www:iscsi> -p <server> -u

And if you want to delete it permanently:

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iscsiadm -m node -T <iqn.2012-02.fr.deimos.www:iscsi> -p <server> -o delete

Resources

For additional resources on this topic, you might want to consult similar documentation on iSCSI setup for other Linux distributions.

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Last updated 04 Jun 2013, 14:04 CEST. history