iSCSI administration on Ubuntu - Quick Start
This post get's you started with iSCSI administration on an Ubuntu machine. Although I have used Ubuntu Trusty (14.04) version, it should work with Precise (12.04) too, with the latest packages.
Prerequisites
Make sure you have atleast a little idea of what these terms mean: iSCSI, LUN, IQN, initiator, target and portal. Google and wikipedia are your friends.
A quick summary:
There are two parts of iSCSI communication - initiator and target. So let's take an example. There is a storage server in your company, where you have a ‘drive’ for your team. The storage server is the ‘target’, and your laptop, where you'll mount the drive to access it's contents is the ‘initiator’. In other words, target is like a ‘server’ which stores data, and allows initiators (think ‘clients’) to connect to it.
In this short hands-on introduction, we'll use the same Ubuntu machine as target as well as initiator. We can use a file as the storage behind the target, but this post also shows how to use LVM logical volume as the backing store for the iSCSI target.
Actually, we'll back the logical volume (LV) with a file, as shown in this, so essentially we're just using ‘file as a backing store for targets’ but in a roundabout way :)
OK, let's get started. Make sure you execute all the following commands as root user.
First install the required dependencies
apt-get install lvm2 tgt open-iscsi
Initialize logical volume
Create a file of 1GB, create a volume group over it, and then over it, create a 400MB logical volume, and see if it got created or not
root@ra:~# truncate --size 1G backingfile
root@ra:~# sudo losetup --find --show backingfile
/dev/loop0
root@ra:~# sudo vgcreate myvg /dev/loop0
No physical volume label read from /dev/loop0
Physical volume "/dev/loop0" successfully created
Volume group "myvg" successfully created
root@ra:~# sudo lvcreate --size 400M --name mylv myvg
Logical volume "mylv" created
root@ra:~# lvs
LV VG Attr LSize Pool Origin Data% Move Log Copy% Convert
mylv myvg -wi-a---- 400.00m
Target administration
Now let's create a target, with target ID 1, and give it an IQN (iSCSI
Qualified Name) iqn.2001-04.example.com:your.first.iscsi.target:
tgtadm --lld iscsi --op new --mode target --tid 1 -T iqn.2001-04.example.com:your.first.iscsi.target
List the target, see it's properties:
root@ra:~# tgtadm --lld iscsi --op show --mode target
Target 1: iqn.2001-04.example.com:your.first.iscsi.target
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
SWP: No
Thin-provisioning: No
Backing store type: null
Backing store path: None
Backing store flags:
Account information:
ACL information:
You can see there is a LUN, LUN 0 attached to the target. Let's attach our
logical volume mylv as LUN 1 to the target.
tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b /dev/myvg/mylv
Here, actually you could've attached a flat file as a LUN to the target. So you
could've skipped all the intermediate steps and attached the backingfile
directly to the target like this:
tgtadm --lld iscsi --op new --mode logicalunit --tid 1 --lun 1 -b backingfile
A backing file would've been good enough for this demo, but you know the benefits of logical volume isn't it? :)
Okay, let's see if the LUN got created:
root@ra:~# tgtadm --lld iscsi --op show --mode target
Target 1: iqn.2001-04.example.com:your.first.iscsi.target
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
SWP: No
Thin-provisioning: No
Backing store type: null
Backing store path: None
Backing store flags:
LUN: 1
Type: disk
SCSI ID: IET 00010001
SCSI SN: beaf11
Size: 419 MB, Block size: 512
Online: Yes
Removable media: No
Prevent removal: No
Readonly: No
SWP: No
Thin-provisioning: No
Backing store type: rdwr
Backing store path: /dev/myvg/mylv
Backing store flags:
Account information:
ACL information:
Now let's allow all initiators to bind to this target:
tgtadm --lld iscsi --op bind --mode target --tid 1 -I ALL
We're done with the ‘target’ side now. You can check, using netstat that port
3260, the default port, is now open. Note that all our commands so far started with
tgtadm, i.e., the target administration utility.
Initiator administration
Now let's start from the ‘initiator’ end. We'll behave as if we're a client trying to connect to the server – the target.
Discover all the targets on our local machine (127.0.0.1).
root@ra:~# sudo iscsiadm --mode discovery --type sendtargets --portal 127.0.0.1
127.0.0.1:3260,1 iqn.2001-04.example.com:your.first.iscsi.target
From the client perspective, we're now able to see a target. Let's login into that target
root@ra:~# sudo iscsiadm --mode node --targetname iqn.2001-04.example.com:your.first.iscsi.target --portal 127.0.0.1:3260 --login
Logging in to [iface: default, target: iqn.2001-04.example.com:your.first.iscsi.target, portal: 127.0.0.1,3260] (multiple)
Login to [iface: default, target: iqn.2001-04.example.com:your.first.iscsi.target, portal: 127.0.0.1,3260] successful.
After logging in, the target will be visible in the client's system as a new
device. Running a fdisk -l shows that there is a new device /dev/sda is now
present.
root@ra:~# fdisk -l
Disk /dev/vda: 57.1 GB, 57076908032 bytes
255 heads, 63 sectors/track, 6939 cylinders, total 111478336 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x0001cd46
Device Boot Start End Blocks Id System
/dev/vda1 * 2048 106520575 53259264 83 Linux
/dev/vda2 106522622 111476735 2477057 5 Extended
/dev/vda5 106522624 111476735 2477056 82 Linux swap / Solaris
Disk /dev/mapper/myvg-mylv: 419 MB, 419430400 bytes
255 heads, 63 sectors/track, 50 cylinders, total 819200 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/mapper/myvg-mylv doesn't contain a valid partition table
Disk /dev/sda: 419 MB, 419430400 bytes
13 heads, 62 sectors/track, 1016 cylinders, total 819200 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x00000000
Disk /dev/sda doesn't contain a valid partition table
Now we just need to format this device with a filesystem, say EXT4, and then mount it at some location to start using it!
root@ra:~# sudo mkfs.ext4 /dev/sda
mke2fs 1.42.9 (4-Feb-2014)
/dev/sda is entire device, not just one partition!
Proceed anyway? (y,n) y
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
102400 inodes, 409600 blocks
20480 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67633152
50 block groups
8192 blocks per group, 8192 fragments per group
2048 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729, 204801, 221185, 401409
Allocating group tables: done
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
root@ra:~# mkdir tempmount
root@ra:~# mount /dev/sda tempmount/
root@ra:~# cd tempmount/
root@ra:~/tempmount# ls
lost+found
root@ra:~/tempmount#
Destruction
The simplest way to get rid of all the things you've created is to unmount the device, and restart the system.
Aaand done!
Cheers!