Using iSCSI On Ubuntu 10.04 (Initiator And Target)

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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 the IncomingUser 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:~#