Thursday, April 19, 2012

Using iSCSI On Debian Squeeze (Initiator And Target)


This guide explains how you can set up an iSCSI target and an iSCSI initiator (client), both running Debian Squeeze. 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 Debian Squeeze servers here:
  • server1.example.com (Initiator): IP address 192.168.0.100
  • server2.example.com (Target): IP address 192.168.0.101

2 Setting Up The Target (server2)

server2:
First we set up the target (server2):
apt-get install iscsitarget iscsitarget-dkms
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/iet/ietd.conf...
vi /etc/iet/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.[: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)...
vi /etc/iet/initiators.allow
[...]
iqn.2001-04.com.example:storage.lun1 192.168.0.100
... and start the target:
/etc/init.d/iscsitarget start

3 Setting Up The Initiator (server1)

server1:
On server1, we install the initiator:
apt-get 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: 0x00029d5c

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        3793    30461952   83  Linux
/dev/sda2            3793        3917      992257    5  Extended
/dev/sda5            3793        3917      992256   82  Linux swap / Solaris

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
root@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.
root@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: 0x00029d5c

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        3793    30461952   83  Linux
/dev/sda2            3793        3917      992257    5  Extended
/dev/sda5            3793        3917      992256   82  Linux swap / Solaris

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: 0x45bc2c81

   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/sda1 on / type ext3 (rw,errors=remount-ro)
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
/dev/sdb1 on /mnt type ext4 (rw)
root@server1:~#
... and
df -h
root@server1:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              29G  807M   27G   3% /
tmpfs                 249M     0  249M   0% /lib/init/rw
udev                  244M  108K  244M   1% /dev
tmpfs                 249M     0  249M   0% /dev/shm
/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
root@server1:~# mount
/dev/sda1 on / type ext3 (rw,errors=remount-ro)
tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
proc on /proc type proc (rw,noexec,nosuid,nodev)
sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
udev on /dev type tmpfs (rw,mode=0755)
tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
/dev/sdb1 on /storage type ext4 (rw,_netdev)
root@server1:~#
df -h
root@server1:~# df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda1              29G  807M   27G   3% /
tmpfs                 249M     0  249M   0% /lib/init/rw
udev                  244M  108K  244M   1% /dev
tmpfs                 249M     0  249M   0% /dev/shm
/dev/sdb1              20G  172M   19G   1% /storage
root@server1:~#

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