Ubuntu Tips And Tricks

This guide explains how you can set up an iSCSI target and an iSCSI initiator (client), both running Ubuntu 10.04. The iSCSI protocol is a storage area network (SAN) protocol which allows iSCSI initiators to use storage devices on the (remote) iSCSI target using normal ethernet cabling. To the iSCSI initiator, the remote storage looks like a normal, locally-attached hard drive.

I do not issue any guarantee that this will work for you!

1 Preliminary Note

I'm using two Ubuntu 10.04 servers here:

server1.example.com (Initiator): IP address 192.168.0.100
server2.example.com (Target): IP address 192.168.0.101

Because we will run all the steps from this tutorial with root privileges, we can either prepend all commands in this tutorial with the string sudo, or we become root right now by typing

sudo su

2 Setting Up The Target (server2)

server2:

First we set up the target (server2):

aptitude install iscsitarget

Open /etc/default/iscsitarget...

vi /etc/default/iscsitarget

... and set ISCSITARGET_ENABLE to true:

ISCSITARGET_ENABLE=true

We can use unused logical volumes, image files, hard drives (e.g. /dev/sdb), hard drive partitions (e.g. /dev/sdb1) or RAID devices (e.g. /dev/md0) for the storage. In this example I will create a logical volume of 20GB named storage_lun1 in the volume group vg0:

lvcreate -L20G -n storage_lun1 vg0

(If you want to use an image file, you can create it as follows:

mkdir /storage
dd if=/dev/zero of=/storage/lun1.img bs=1024k count=20000

This creates the image file /storage/lun1.img with a size of 20GB.

)

Next we edit /etc/ietd.conf...

vi /etc/ietd.conf

... and comment out everything in that file. At the end we add the following stanza:

[...]
Target iqn.2001-04.com.example:storage.lun1
        IncomingUser someuser secret
        OutgoingUser
        Lun 0 Path=/dev/vg0/storage_lun1,Type=fileio
        Alias LUN1
        #MaxConnections  6

The target name must be a globally unique name, the iSCSI standard defines the "iSCSI Qualified Name" as follows: iqn.yyyy-mm.<reversed domain name>[:identifier];yyyy-mm is the date at which the domain is valid; the identifier is freely selectable. The IncomingUser line contains a username and a password so that only the initiators (clients) that provide this username and password can log in and use the storage device; if you don't need authentication, don't specify a username and password in theIncomingUser line. In the Lun line, we must specify the full path to the storage device (e.g. /dev/vg0/storage_lun1, /storage/lun1.img, /dev/sdb, etc.).

Now we tell the target that we want to allow connections to the device iqn.2001-04.com.example:storage.lun1 from the IP address 192.168.0.100 (server1.example.com) (comment out the ALL ALL line because that would allow all initiators to connect to all targets)...

vi /etc/initiators.allow

[...]
iqn.2001-04.com.example:storage.lun1 192.168.0.100
#ALL ALL

... and start the target:

/etc/init.d/iscsitarget start

3 Setting Up The Initiator (server1)

server1:

On server1, we install the initiator:

aptitude install open-iscsi

Next we open /etc/iscsi/iscsid.conf...

vi /etc/iscsi/iscsid.conf

... and set node.startup to automatic:

[...]
node.startup = automatic
[...]

Then we restart the initiator:

/etc/init.d/open-iscsi restart

Now we connect to the target (server2) and check what storage devices it has to offer:

iscsiadm -m discovery -t st -p 192.168.0.101

root@server1:~# iscsiadm -m discovery -t st -p 192.168.0.101

192.168.0.101:3260,1 iqn.2001-04.com.example:storage.lun1

root@server1:~#

iscsiadm -m node

root@server1:~# iscsiadm -m node

192.168.0.101:3260,1 iqn.2001-04.com.example:storage.lun1

root@server1:~#

The settings for the storage device iqn.2001-04.com.example:storage.lun1 on 192.168.0.101:3260,1 are stored in the file /etc/iscsi/nodes/iqn.2001-04.com.example:storage.lun1/192.168.0.101,3260,1/default. We need to set the username and password for the target in that file; instead of editing that file manually, we can use the iscsiadm command to do this for us:

iscsiadm -m node --targetname "iqn.2001-04.com.example:storage.lun1" --portal "192.168.0.101:3260" --op=update --name node.session.auth.authmethod --value=CHAP
iscsiadm -m node --targetname "iqn.2001-04.com.example:storage.lun1" --portal "192.168.0.101:3260" --op=update --name node.session.auth.username --value=someuser
iscsiadm -m node --targetname "iqn.2001-04.com.example:storage.lun1" --portal "192.168.0.101:3260" --op=update --name node.session.auth.password --value=secret

Now we can log in, either by running...

iscsiadm -m node --targetname "iqn.2001-04.com.example:storage.lun1" --portal "192.168.0.101:3260" --login

root@server1:~# iscsiadm -m node --targetname "iqn.2001-04.com.example:storage.lun1" --portal "192.168.0.101:3260" --login
Logging in to [iface: default, target: iqn.2001-04.com.example:storage.lun1, portal: 192.168.0.101,3260]
Login to [iface: default, target: iqn.2001-04.com.example:storage.lun1, portal: 192.168.0.101,3260]: successful
root@server1:~#

... or by restarting the initiator:

/etc/init.d/open-iscsi restart

(If you want to log out, you can run

iscsiadm -m node --targetname "iqn.2001-04.com.example:storage.lun1" --portal "192.168.0.101:3260" --logout

)

In the output of

fdisk -l

you should now find a new hard drive (/dev/sdb in this example); that's our iSCSI storage device:

root@server1:~# fdisk -l

Disk /dev/sda: 32.2 GB, 32212254720 bytes
255 heads, 63 sectors/track, 3916 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00016be9

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          32      248832   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              32        3917    31205377    5  Extended
/dev/sda5              32        3917    31205376   8e  Linux LVM

Disk /dev/sdb: 21.5 GB, 21474836480 bytes
64 heads, 32 sectors/track, 20480 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000

Disk /dev/sdb doesn't contain a valid partition table
root@server1:~#

To use that device, we must format it:

fdisk /dev/sdb

server1:~# fdisk /dev/sdb

Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x882944df.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

The number of cylinders for this disk is set to 20480.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:

1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): <-- m
Command action
   a   toggle a bootable flag
   b   edit bsd disklabel
   c   toggle the dos compatibility flag
   d   delete a partition
   l   list known partition types
   m   print this menu
   n   add a new partition
   o   create a new empty DOS partition table
   p   print the partition table
   q   quit without saving changes
   s   create a new empty Sun disklabel
   t   change a partition's system id
   u   change display/entry units
   v   verify the partition table
   w   write table to disk and exit
   x   extra functionality (experts only)

Command (m for help): <-- n
Command action
   e   extended
   p   primary partition (1-4)

<-- p
Partition number (1-4): <-- 1
First cylinder (1-20480, default 1): <-- ENTER
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-20480, default 20480): <-- ENTER
Using default value 20480

Command (m for help): <-- t
Selected partition 1
Hex code (type L to list codes): <-- L

0  Empty           1e  Hidden W95 FAT1 80  Old Minix       be  Solaris boot
1  FAT12           24  NEC DOS         81  Minix / old Lin bf  Solaris
2  XENIX root      39  Plan 9          82  Linux swap / So c1  DRDOS/sec (FAT-
3  XENIX usr       3c  PartitionMagic  83  Linux           c4  DRDOS/sec (FAT-
4  FAT16 <32M      40  Venix 80286     84  OS/2 hidden C:  c6  DRDOS/sec (FAT-
5  Extended        41  PPC PReP Boot   85  Linux extended  c7  Syrinx
6  FAT16           42  SFS             86  NTFS volume set da  Non-FS data
7  HPFS/NTFS       4d  QNX4.x          87  NTFS volume set db  CP/M / CTOS / .
8  AIX             4e  QNX4.x 2nd part 88  Linux plaintext de  Dell Utility
9  AIX bootable    4f  QNX4.x 3rd part 8e  Linux LVM       df  BootIt
a  OS/2 Boot Manag 50  OnTrack DM      93  Amoeba          e1  DOS access
b  W95 FAT32       51  OnTrack DM6 Aux 94  Amoeba BBT      e3  DOS R/O
c  W95 FAT32 (LBA) 52  CP/M            9f  BSD/OS          e4  SpeedStor
e  W95 FAT16 (LBA) 53  OnTrack DM6 Aux a0  IBM Thinkpad hi eb  BeOS fs
f  W95 Ext'd (LBA) 54  OnTrackDM6      a5  FreeBSD         ee  EFI GPT
10  OPUS            55  EZ-Drive        a6  OpenBSD         ef  EFI (FAT-12/16/
11  Hidden FAT12    56  Golden Bow      a7  NeXTSTEP        f0  Linux/PA-RISC b
12  Compaq diagnost 5c  Priam Edisk     a8  Darwin UFS      f1  SpeedStor
14  Hidden FAT16 <3 61  SpeedStor       a9  NetBSD          f4  SpeedStor
16  Hidden FAT16    63  GNU HURD or Sys ab  Darwin boot     f2  DOS secondary
17  Hidden HPFS/NTF 64  Novell Netware  b7  BSDI fs         fd  Linux raid auto
18  AST SmartSleep  65  Novell Netware  b8  BSDI swap       fe  LANstep
1b  Hidden W95 FAT3 70  DiskSecure Mult bb  Boot Wizard hid ff  BBT
1c  Hidden W95 FAT3 75  PC/IX
Hex code (type L to list codes): <-- 83

Command (m for help): <-- w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.
server1:~#

Afterwards, the output of

fdisk -l

should look as follows:

root@server1:~# fdisk -l

Disk /dev/sda: 32.2 GB, 32212254720 bytes
255 heads, 63 sectors/track, 3916 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00016be9

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          32      248832   83  Linux
Partition 1 does not end on cylinder boundary.
/dev/sda2              32        3917    31205377    5  Extended
/dev/sda5              32        3917    31205376   8e  Linux LVM

Disk /dev/sdb: 21.5 GB, 21474836480 bytes
64 heads, 32 sectors/track, 20480 cylinders
Units = cylinders of 2048 * 512 = 1048576 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x725b9dff

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1       20480    20971504   83  Linux
root@server1:~#

Now we create a filesystem on /dev/sdb1...

mkfs.ext4 /dev/sdb1

... and mount it for test purposes:

mount /dev/sdb1 /mnt

You should now see the new device in the outputs of...

mount

root@server1:~# mount
/dev/mapper/server1-root on / type ext4 (rw,errors=remount-ro)
proc on /proc type proc (rw,noexec,nosuid,nodev)
none on /sys type sysfs (rw,noexec,nosuid,nodev)
none on /sys/fs/fuse/connections type fusectl (rw)
none on /sys/kernel/debug type debugfs (rw)
none on /sys/kernel/security type securityfs (rw)
none on /dev type devtmpfs (rw,mode=0755)
none on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=0620)
none on /dev/shm type tmpfs (rw,nosuid,nodev)
none on /var/run type tmpfs (rw,nosuid,mode=0755)
none on /var/lock type tmpfs (rw,noexec,nosuid,nodev)
none on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
none on /var/lib/ureadahead/debugfs type debugfs (rw,relatime)
/dev/sda1 on /boot type ext2 (rw)
/dev/sdb1 on /mnt type ext4 (rw)
root@server1:~#

... and

df -h

root@server1:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/server1-root
                       18G  838M   16G   5% /
none                  243M  180K  242M   1% /dev
none                  247M     0  247M   0% /dev/shm
none                  247M   36K  247M   1% /var/run
none                  247M     0  247M   0% /var/lock
none                  247M     0  247M   0% /lib/init/rw
none                   18G  838M   16G   5% /var/lib/ureadahead/debugfs
/dev/sda1             228M   17M  199M   8% /boot
/dev/sdb1              20G  172M   19G   1% /mnt
root@server1:~#

You can unmount it like this:

umount /mnt

To have the device mounted automatically at boot time, e.g. in the directory /storage, we create that directory...

mkdir /storage

... and add the following line to /etc/fstab:

vi /etc/fstab

[...]
/dev/sdb1       /storage        ext4    defaults,auto,_netdev 0 0

For test purposes, you can now reboot the system:

reboot

After the reboot, the device should be mounted:

mount

df -h

root@server1:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/mapper/server1-root
                       18G  839M   16G   5% /
none                  243M  180K  242M   1% /dev
none                  247M     0  247M   0% /dev/shm
none                  247M   36K  247M   1% /var/run
none                  247M     0  247M   0% /var/lock
none                  247M     0  247M   0% /lib/init/rw
none                   18G  839M   16G   5% /var/lib/ureadahead/debugfs
/dev/sda1             228M   17M  199M   8% /boot
/dev/sdb1              20G  172M   19G   1% /storage
root@server1:~#

Considerations

Remember that iSCSI gives raw filesystem access to other machines, and that Windows doesn't support ext2/3 filesystems, so any devices being shared to Windows machines will need to be formatted as FAT(12/16/32) or NTFS. Linux's NTFS support is reasonable enough these days for this to not be too much of a problem, however.

Installation

Checkout a copy of the source from the SVN URL given on the iSCSI Enterprise Target SVN site:

svn checkout svn://svn.berlios.de/iscsitarget/trunk

Change into the trunk directory:

cd trunk

Make and install iSCSI Enterprise Target:

make
make install

Copy the configuration files into /etc/:

cp -r etc/* /etc/

Configuration

Server (Target)

Change into the /etc/ directory:

cd /etc

Edit ietd.conf:

vi ietd.conf

- Change the "Target" line to match your setup. The format is "Target iqn.2008-02.net.sihnon.jiangyin.hex:hex.music", where:
  - "2008" is the current year
  - "02" is the current month
  - "net.sihnon.jiangyin.hex" is the reversed domain name of the host
  - "hex.music" is the identifier for this target (i.e. disk). It can be anything you like, but must be unique.
- Uncomment the "Lun 0 Path=/dev/sdc,Type=fileio" line and change the "Path" to the physical, /dev/..., path to the device, e.g. /dev/hda1.
Edit initiators.allow:

vi initiators.allow

- For testing/debugging purposes, simply add:

ALL ALL

to the bottom of the file and save it.

Restart the iSCSI service:

/etc/init.d/iscsi-target restart

Windows Client (Initiator)

Assuming that the iSCSI Initiator is already installed.

Load the iSCSI Initiator Properties applet in Control Panel.
On the General tab, click the "Change" button to rename the Initiator. Change its name to the same as you named the Target in the server configuration, minus the identifier; e.g. "iqn.2008-02.net.sihnon.jiangyin.hex".
On the Discover tab, click the "Add Portal" button to add a new Target Portal. Enter the IP address of the Target server, leaving the port at the default, then click OK.
Switch to the Targets tab and click the Refresh button. Your iSCSI Target server's target devices should appear in the list. Assuming they do, click one to select it, then click the "Log on..." button and click "OK" on the dialog that pops up.
You should now be connected to that iSCSI drive.
Open Control Panel -> Administrative Tools -> Computer Management -> Disk Management, or run "diskmgmt.msc", and the new iSCSI disk should be displayed. It will need to be formatted with a filesystem that Windows understands (if it isn't already) before it can be mounted, though.

References

http://www.nge.com.au/index.php?next_page=res/tech_articles/iscsi_enterprise_target_ubuntu_6.06_LTS.php

Ubuntu Tips And Tricks

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Using iSCSI On Ubuntu 10.04 (Initiator And Target)