Linux tgtadm: Setup iSCSI Target ( SAN )

last updated in Categories CentOS, data center, Debian Linux, fedora linux, File system, GNU/Open source, Hardware, Linux, Storage

Linux target framework (tgt) aims to simplify various SCSI target driver (iSCSI, Fibre Channel, SRP, etc) creation and maintenance. The key goals are the clean integration into the scsi-mid layer and implementing a great portion of tgt in user space.

The developer of IET is also helping to develop Linux SCSI target framework (stgt) which looks like it might lead to an iSCSI target implementation with an upstream kernel component. iSCSI Target can be useful:

a] To setup stateless server / client (used in diskless setups).
b] Share disks and tape drives with remote client over LAN, Wan or the Internet.
c] Setup SAN – Storage array.
d] To setup loadbalanced webcluser using cluster aware Linux file system etc.

In this tutorial you will learn how to have a fully functional Linux iSCSI SAN using tgt framework.

iSCSI target (server)

Storage resource located on an iSCSI server known as a “target”. An iSCSI target usually represents nothing but hard disk storage. As with initiators, software to provide an iSCSI target is available for most mainstream operating systems.

iSCSI initiator (client)

An initiator functions as an iSCSI client. An initiator typically serves the same purpose to a computer as a SCSI bus adapter would, except that instead of physically cabling SCSI devices (like hard drives and tape changers), an iSCSI initiator sends SCSI commands over an IP network.

Debian / Ubuntu Linux Install tgt

Type the following command to install Linux target framework user-space tools:
$ sudo apt-get install tgt

CentOS / RHEL / Red Hat Linux Install tgt

RHEL 5.2 and older version do not have tgt tools. However, RHEL 5.3 (preview version) comes with tgt tools.

tgtadm – Linux SCSI Target Administration Utility

tgtadm is used to monitor and modify everything about Linux SCSI target software: targets, volumes, etc. This tool allows a system to serve block-level SCSI storage to other systems that have a SCSI initiator. This capability is being initially deployed as a Linux iSCSI target, serving storage over a network to any iSCSI initiator.

Start tgtd

To start the tgtd, enter:
# /usr/sbin/tgtd
Under RHEL 5.3 to start the tgtd service, enter:
# /etc/init.d/tgtd start

Define an iscsi target name

The following example creates a target with id 1 (the iqn is 19 iqn.2001-04.com.example:storage.disk2.amiens.sys1.xyz) and adds a 20 logical unit (backed by /dev/hdc1) with lun 1.
# tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.2001-04.com.example:storage.disk2.amiens.sys1.xyz

To view the current configuration, enter:
# tgtadm --lld iscsi --op show --mode target
Sample output:

Target 1: iqn.2001-04.com.example:storage.disk1.amiens.sys1.xyz
    System information:
        Driver: iscsi
        Status: running
    I_T nexus information:
    LUN information:
        LUN: 0
            Type: controller
            SCSI ID: deadbeaf1:0
            SCSI SN: beaf10
            Size: 0
            Online: No
            Poweron/Reset: Yes
            Removable media: No
            Backing store: No backing store
    Account information:
    ACL information:

Add a logical unit to the target (/dev/sdb1):
# tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b /dev/sdb1

A note about home computer / test system

Most production boxes will only use iSCSI root with real iSCSI devices, but for testing purposes it can be quite useful to set up an iSCSI target on your image server. This is useful for testing and learning iSCSI target and iSCSI initiator at home, simply use filesystem for testing purpose. Use dd command to create diskbased filesystem:
# dd if=/dev/zero of=/fs.iscsi.disk bs=1M count=512
Add /fs.iscsi.disk as a logical unit to the target:
# tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b /fs.iscsi.disk
Now, you should able to view details:
# tgtadm --lld iscsi --op show --mode target
Sample output:

Target 1: iqn.2001-04.com.example:storage.disk1.amiens.sys1.xyz
    System information:
        Driver: iscsi
        Status: running
    I_T nexus information:
    LUN information:
        LUN: 0
            Type: controller
            SCSI ID: deadbeaf1:0
            SCSI SN: beaf10
            Size: 0
            Online: No
            Poweron/Reset: Yes
            Removable media: No
            Backing store: No backing store
        LUN: 1
            Type: disk
            SCSI ID: deadbeaf1:1
            SCSI SN: beaf11
            Size: 512M
            Online: Yes
            Poweron/Reset: Yes
            Removable media: No
            Backing store: /fs.iscsi.disk
    Account information:
    ACL information:

A Note About Selinux

Renout Gerrits adds – On RHEL and friends you will run into problems if selinux is enabled if using files. While adding a logicalunit to a target you will get the error: ‘tgtadm: invalid request’. A bit of a misguiding error. fixed by setting the correct context:
# semanage fcontext -a -t tgtd_var_lib_t /fs.iscsi.disk
# restorecon -Rv /fs.iscsi.disk

Accept iSCSI Target

To enable the target to accept any initiators, enter:
# tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
This should open network port # 3260:
# netstat -tulpn | grep 3260
Sample output:

tcp        0      0 0.0.0.0:3260            0.0.0.0:*               LISTEN      27328/tgtd
tcp6       0      0 :::3260                 :::*                    LISTEN      27328/tgtd

And you are done. Your system is configured as iSCSI Target. Remote client computer can access this computers hard disk over network. Your can use cluster aware filesystem to setup real shared storage for small business. Open TCP port 3260 in your firewall, if required.

How do I access iSCSI Target (server) via iSCSI initiator (client)?

See detailed os specific iSCSI initiator instuctions:

  1. RHEL 4 or RHEL 5 Linux iSCSI initiator tutorial.
  2. Debian Linux iSCSI initiator tutorial.
  3. FreeBSD iSCSI initiator tutorial.
  4. Windows iSCSI initiator tutorial.

Following is a quick way to access iSCSI target, under RHEL 5. Let us say your server iSCSI Target IP is 192.168.1.2. Type the following command to discover targets at a given IP address such as 192.168.1.2 (use 127.0.0.1 if you are testing it from same computer):
# iscsiadm --mode discovery --type sendtargets --portal 192.168.1.2
OR
# iscsiadm --mode discovery --type sendtargets --portal 127.0.0.1
Sample output:

127.0.0.1:3260,1 iqn.2001-04.com.example:storage.disk1.amiens.sys1.xyz

Login to the iscsi target session:
# iscsiadm --mode node --targetname iqn.2001-04.com.example:storage.disk1.amiens.sys1.xyz --portal 192.168.1.2:3260 --login
OR
# iscsiadm --mode node --targetname iqn.2001-04.com.example:storage.disk1.amiens.sys1.xyz --portal 127.0.0.1:3260 --login
Verify that login was successful:
# tail -f /var/log/messages
Sample output:

Nov 11 07:34:04 vivek-desktop kernel: [ 9039.562312] scsi 6:0:0:1: Direct-Access     IET      VIRTUAL-DISK     0001 PQ: 0 ANSI: 5
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.572268] sd 6:0:0:1: [sdc] 1048576 512-byte hardware sectors (537 MB)
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.572374] sd 6:0:0:1: [sdc] Write Protect is off
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.572530] sd 6:0:0:1: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.572715] sd 6:0:0:1: [sdc] 1048576 512-byte hardware sectors (537 MB)
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.572790] sd 6:0:0:1: [sdc] Write Protect is off
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.572940] sd 6:0:0:1: [sdc] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.572946]  sdc: unknown partition table
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.573492] sd 6:0:0:1: [sdc] Attached SCSI disk
Nov 11 07:34:04 vivek-desktop kernel: [ 9039.573593] sd 6:0:0:1: Attached scsi generic sg4 type 0

sdc is new scsi disk. You may need to restart iSCSI to probe partition and check disks:
# service iscsi restart
# partprobe
# fdisk -l
You can now create parition and mount file system using usual fdisk and mkfs.ext3 commands:
# fdisk /dev/sdc
# mkfs.ext3 /dev/sdc1mkdir /iscsi
# mkdir /iscsi
# mount /dev/sdc1 /iscsi
# df -H
Sample output:

Filesystem             Size   Used  Avail Use% Mounted on
/dev/sda2               99G    30G    64G  32% /
tmpfs                  1.1G      0   1.1G   0% /lib/init/rw
varrun                 1.1G   361k   1.1G   1% /var/run
varlock                1.1G      0   1.1G   0% /var/lock
udev                   1.1G   2.9M   1.1G   1% /dev
tmpfs                  1.1G   312k   1.1G   1% /dev/shm
/dev/sda1              105G    32G    73G  31% /media/sda1
/dev/sda5              294G   275G    20G  94% /share
/dev/sdb2              247G   119G   116G  51% /disk1p2
/dev/sdc1              520M    11M   483M   3% /iscsi

References:

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

30 comment

  5. hi,guys,i have a question,
    when i setup a iscsi target then export an iscsi device,
    then i discovery the target device on two diffenence initoator ,and mount the device
    the in node a i create a file in the device which was iscsi device ,and then i think i will the file in the node b the iscsi device ,but i cann’t see the file .i get lost.

  6. xiaolong
    iscsi cannot do file sharing. because, unlike nfs, there is no locking.
    just like fc san.
    you can make a lun into a zone visible to more than 1 server, you can even access the lun from them. but you do not do that because it is just a raw access. not locking.

  7. hi,

    iscsi can export devices, but not filesystems. if you want more than one server access the same filesystem, you have to go on gfs2 or ocfs2. it’s not so difficult to setup 😉

    and what about iet vs tgt? what’s the best iscsi target for linux?

    many thanks,

    ftaurino

  10. I also would like to know the answer to Vincents question – how to make it survive a reboot

    Great post – thanks!

  11. Vincent

    For making the setup persistent over reboot type this command:

    # tgt-admin –dump > /etc/tgt/targets.conf

    # chkconfig tgtd on

  12. How would you make a boot LUN if all you can set it is LUN 1? Or is there anyway to make it bootable? The only OS I’ve been able to boot from that LUN is SLES 11 SP1. Tried RHEL 5 and Win2k8 and both could not locate the LUN.

  13. Thanks for a good tutorial. First one I found that was actually helpful in getting everything setup, bookmarked.

  14. @John

    If you are booting Win2k8 “from SAN” per se, the boot partition has to have a LUN # that is neither 0 or 1 and is not more than 3 digits (ex. LUN 100, 101).

  15. I’m on CentOS 5.4 and when i run this command getting below error:
    tgtadm –lld iscsi –op new –mode target –tid 1 -T iqn.2001-04.com.example:storage.disk2.amiens.sys1.xyz

    tgtadm: unrecognized option ‘iscsi’
    try ‘tgtadm –help’

    can you please help? Thanks

    1. At first glance it sounds like something isn’t correct with the iscsi utilities, I’d try reinstalling them.

      yum reinstall iscsi-initiator-utils scsi-target-utils

    2. you should add the sudo command as
      sudo tgtadm –lld iscsi –op new –mode target –tid 1 -T iqn.2001-04.com.example:storage.disk2.amiens.sys1.xyz

  16. Thanks for the quick response. I was missing “iscsi-initiator-utils”. After installing it “tgtadm –lld iscsi –op show –mode target” started showing results. But is not persistent after reboot, I did try steps from above comment(# tgt-admin –dump > /etc/tgt/targets.conf and # chkconfig tgtd on) and it still doesn’t work. I’m using CentOS 5.4. Thanks again for the wonderful post.

    1. Never mind. I re-did the configuration from scratch and now it is persistent after reboots. Thanks again

  18. It is so long as you remember to use a locking filesystem properly. Something like drbl. Can’t say I’ve ever set one up so that’s all for now.

  19. It’s really nice tutorial. I am doing a LAB setup. Where I am using Open Filer for storage. In 2 node RHEL5 systems I need to share the same LUN. using “iscsiadm –mode discovery –type sendtargets –portal 192.168.1.2” I am able to discover the LUN in both of the systems.

  20. I have implement one iscsi target . Now wont to implement two iscsi targets with load balancing. is it posible to do so?…..

    1. is it is …
      you nee to use mdadm or LVM mirroring , discover the 2 devices then set up a single device to mount , if you are using a high storage system with ISCSI capabilites then you can use multipath to bind the 2 devices.
      before that you need to make sure the initiator have 2 different IP’s (of the same storage ) to talk with.

  21. Hello,

    Is it possible to connect 2 initiators on the same target (initiators and target on centos 6)?, each initiator accessing different block device of the target?

    I have tried to configured the /etc/targets.conf using initiator-address ,and also using incominguser password, but it seems these are global variable and can not be defined per lun. Any ideas?

  22. I have a rhel6.1 setup and the below command is not working.. is it a BUG.

    /usr/sbin/tgtadm –lld iscsi –op new –mode logicalunit –tid 1 –lun 1 -b /mnt1/lun10
    return code 22
    ==============================================
    tgtadm: invalid request
    ==============================================

  23. faced

    NO Portal Found Error

    Fixed the issue using your Command

    tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL

    Thousands of Thanks …

  24. When I issue the command “/usr/sbin/tgtd” I get the following:

    (null): iscsi_tcp_init_portal(227) unable to bind server socket, Address already in use
    (null): iscsi_tcp_init_portal(227) unable to bind server socket, Address already in use
    (null): iscsi_add_portal(275) failed to create/bind to portal (null):3260
    librdmacm: couldn’t read ABI version.
    librdmacm: assuming: 4
    CMA: unable to get RDMA device list
    (null): iser_ib_init(3263) Failed to initialize RDMA; load kernel modules?
    (null): fcoe_init(214) (null)
    (null): fcoe_create_interface(171) no interface specified.
    (null): ipc_init(635) can’t bind a socket, Address already in use

    Any idea what I can do?
    Running Linux Mint Maya (13) Kernel 3.2.0-23-generic
    Thanks

  25. Hello,

    I did the following procedure:
    tgtadm –lld iscsi –mode target –op new –tid 1 –targetname iqn.2014-09.local.vclass:tg0
    tgtadm –lld iscsi –op new –mode logicalunit –tid 1 –lun 1 –backing-store /dev/sdg
    tgtadm –lld iscsi –op new –mode logicalunit –tid 1 –lun 2 –backing-store /dev/sdh
    tgtadm –lld iscsi –op new –mode logicalunit –tid 1 –lun 3 –backing-store /dev/sdi
    tgtadm –lld iscsi –op new –mode logicalunit –tid 1 –lun 4 –backing-store /dev/sdj
    tgtadm –lld iscsi –mode target –op new –tid 2 –targetname iqn.2014-09.local.vclass:tg1
    tgtadm –lld iscsi –mode target –op new –tid 3 –targetname iqn.2014-09.local.vclass:tg2
    tgtadm –lld iscsi –op new –mode logicalunit –tid 2 –lun 5 –backing-store /dev/sde
    tgtadm –lld iscsi –op new –mode logicalunit –tid 3 –lun 5 –backing-store /dev/sdf
    tgtadm –lld iscsi –op bind –mode target –tid 2 –initiator-address 172.20.10.61
    tgtadm –lld iscsi –op bind –mode target –tid 3 –initiator-address 172.20.10.62
    tgtadm –mode target –op show
    tgt-admin –dump > /etc/tgt/targets.conf

    and the tgtadm –mode target –op show output was as shown bellow:
    [root@iscsi ~]# tgtadm –mode target –op show
    Target 1: iqn.2014-09.local.vclass:tg0
    System information:
    Driver: iscsi
    State: ready
    I_T nexus information:
    LUN information:
    LUN: 0
    Type: controller
    SCSI ID: IET 00010000
    SCSI SN: beaf10
    Size: 0 MB, Block size: 1
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: null
    Backing store path: None
    Backing store flags:
    LUN: 1
    Type: disk
    SCSI ID: IET 00010001
    SCSI SN: beaf11
    Size: 10737 MB, Block size: 512
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: rdwr
    Backing store path: /dev/sdg
    Backing store flags:
    LUN: 2
    Type: disk
    SCSI ID: IET 00010002
    SCSI SN: beaf12
    Size: 10737 MB, Block size: 512
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: rdwr
    Backing store path: /dev/sdh
    Backing store flags:
    LUN: 3
    Type: disk
    SCSI ID: IET 00010003
    SCSI SN: beaf13
    Size: 10737 MB, Block size: 512
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: rdwr
    Backing store path: /dev/sdi
    Backing store flags:
    LUN: 4
    Type: disk
    SCSI ID: IET 00010004
    SCSI SN: beaf14
    Size: 10737 MB, Block size: 512
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: rdwr
    Backing store path: /dev/sdj
    Backing store flags:
    Account information:
    ACL information:
    Target 2: iqn.2014-09.local.vclass:tg1
    System information:
    Driver: iscsi
    State: ready
    I_T nexus information:
    LUN information:
    LUN: 0
    Type: controller
    SCSI ID: IET 00020000
    SCSI SN: beaf20
    Size: 0 MB, Block size: 1
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: null
    Backing store path: None
    Backing store flags:
    LUN: 5
    Type: disk
    SCSI ID: IET 00020005
    SCSI SN: beaf25
    Size: 10737 MB, Block size: 512
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: rdwr
    Backing store path: /dev/sde
    Backing store flags:
    Account information:
    ACL information:
    172.20.10.61
    Target 3: iqn.2014-09.local.vclass:tg2
    System information:
    Driver: iscsi
    State: ready
    I_T nexus information:
    LUN information:
    LUN: 0
    Type: controller
    SCSI ID: IET 00030000
    SCSI SN: beaf30
    Size: 0 MB, Block size: 1
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: null
    Backing store path: None
    Backing store flags:
    LUN: 5
    Type: disk
    SCSI ID: IET 00030005
    SCSI SN: beaf35
    Size: 10737 MB, Block size: 512
    Online: Yes
    Removable media: No
    Prevent removal: No
    Readonly: No
    Backing store type: rdwr
    Backing store path: /dev/sdf
    Backing store flags:
    Account information:
    ACL information:
    172.20.10.62

    My intention is that all LUN IDs should be different per host, so tg0 will serves shared LUNs 1,2,3 and 4 and tg1 serves LUN 5 to host 172.20.10.61 and tg2 serves LUN 5 to host 172.20.10.62. I am using CentOS 6.5
    After reboot tg1 and tg2 presents the LUNs both with LUN ID 1.
    Also added LUN 5 to both targets in /etc/tgt/targets.conf and after reboot ignores the instruction and still presents with LUN ID 1.

    /etc/tgt/targets.conf bellow:

    Default-driver iscsi

    backing-store /dev/sdf
    LUN 5
    initiator-address 172.20.10.62

    backing-store /dev/sde
    LUN 5
    initiator-address 172.20.10.61

    backing-store /dev/sdg
    backing-store /dev/sdh
    backing-store /dev/sdi
    backing-store /dev/sdj

    Please, can anyone be so kind and help me to fix the LUN IDs?

    Thank you in advance.

  26. Hi,
    Using Centos nodes & Openfiler. Quorum disk shows up as sdb on node1 and the quorum disk is sdc on node2. Similarly shared-disk is sdc on node1 and sdb on node2. Getting a couple of disks for “quorum” disk and “shared disk” i.e a total of 4 disks on 1 node each…maybe the 2 interfaces which I am using on the virtual-box is giving this o/p !!!!.I have tried rediscovering the targets(logout,delete,discover & relogin) and reloading the iscsi service as well. Is there any way to fix this.

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