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:
- RHEL 4 or RHEL 5 Linux iSCSI initiator tutorial.
- Debian Linux iSCSI initiator tutorial.
- FreeBSD iSCSI initiator tutorial.
- 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:
- man page tgtadm
- tgt project
- iSCSI article from the wikipedia
This blog post is 4 of 4 in the " Linux iSCSI Initiator (SCSI protocol over TCP/IP networks) Tutorial" series. Keep reading the rest of the series:
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