Less known Solaris Features...

File based iSCSI target

One way to provide for storage for an iSCSI target. You can use files for this task. Okay, we have to login as root on theoden:

# mkdir -p /var/iscsitargets
# iscsitadm modify admin -d /var/iscsitargets

At first we´ve created an directory to keep the files, then we tell the target daemon to use this for storing the target.After this we ca create the target:

# iscsitadm create target --size 128m smalltarget

Now we can check for the iSCSI Target.

# iscsitadm list target -v smalltarget
Target: smalltarget
iSCSI Name: iqn.1986-03.com.sun:02:3898c6a7-1f43-e298-e189-83d10f88131d.smalltarget
Connections: 0
ACL list:
TPGT list:
LUN information:
LUN: 0
GUID: 0100001c42e9f21a00002a0047e45145
VID: SUN
PID: SOLARIS
Type: disk
Size: 128M
Status: offline

Now we switch to the server we use as an initiator. Let´s scan for new devices on gandalf. As we´ve activated the discovery of targets before, we´ve just have to scan for new devices.

# devfsadm -c iscsi -C
# format
Searching for disks...done


AVAILABLE DISK SELECTIONS:
0. c0d0
/pci@0,0/pci-ide@1f,1/ide@0/cmdk@0,0
1. c1d0
/pci@0,0/pci-ide@1f,1/ide@1/cmdk@0,0
2. c2t0100001C42E9F21A00002A0047E39E34d0
/scsi_vhci/disk@g0100001c42e9f21a00002a0047e39e34
3. c2t0100001C42E9F21A00002A0047E45145d0
/scsi_vhci/disk@g0100001c42e9f21a00002a0047e45145
Specify disk (enter its number):
Specify disk (enter its number): ^C
#

Et voila, an additional LUN is available on our initiator.

Thin-provisioned target backing store

One nice thing about ZFS is it´s ability to provide thin provisioned emulated zfs volumes (zvol). You can configure a volume of an larger size than the physical storage you have available. This is useful, when you want to have an volume in it´s final size (because resizing would be a pain in the a...) but don´t want do spend the money for the disks because you know that much less storage would be needed at first.

It´s really easy to create such a kind of a zvol:

# zfs create -s -V 2g testpool/bigvolume

That´s all. The difference is the small -s. It tells ZFS to create an sparse (aka thin) provisioned volume.

Well, I won´t enable iSCSI for this by shareiscsi=on itself. I will configure this manually. As normal volumes zvols are available within the /dev tree of your filesystem:

# ls -l /dev/zvol/dsk/testpool
total 4
lrwxrwxrwx 1 root root 35 Mar 22 02:09 bigvolume -> ../../../../devices/pseudo/zfs@0:2c
lrwxrwxrwx 1 root root 35 Mar 21 12:33 zfsvolume -> ../../../../devices/pseudo/zfs@0:1c

Okay, we can use this devices as a backing store for an iSCSI target as well. We´ve created a zvol bigvolume within the zpool testpool. Thus the device is /dev/zvol/dsk/testpool/bigvolume:

# iscsitadm create target -b /dev/zvol/dsk/testpool/bigvolume bigtarget

Okay, i´m swiching to my root shell on the initiator. Again we scan for devices:

# devfsadm -c iscsi -C
# format
Searching for disks...done


AVAILABLE DISK SELECTIONS:
0. c0d0
/pci@0,0/pci-ide@1f,1/ide@0/cmdk@0,0
1. c1d0
/pci@0,0/pci-ide@1f,1/ide@1/cmdk@0,0
2. c2t0100001C42E9F21A00002A0047E39E34d0
/scsi_vhci/disk@g0100001c42e9f21a00002a0047e39e34
3. c2t0100001C42E9F21A00002A0047E45DB2d0
/scsi_vhci/disk@g0100001c42e9f21a00002a0047e45db2


Let´s create an zpool:

# zpool create zfsviaiscsi_thin c2t0100001C42E9F21A00002A0047E45DB2d0
# zpool list
NAME SIZE USED AVAIL CAP HEALTH ALTROOT
zfsviaiscsi 187M 112K 187M 0% ONLINE -
zfsviaiscsi_thin 1.98G 374K 1.98G 0% ONLINE -

Do you remember, that we used four 128 MB files as the devices for our zpool on our target. Well, you have an 1.98G filesytem running on this files. You can add more storage to the zpool on the target and you have nothing to do on the initiator. Not a real kicker for ZFS, but imagine the same for other filesystem that can´t be grown so easy like a zpool.