The iSCSI Datastore 3.4
The iSCSI datastore driver provides OpenNebula with the possibility of using block-devices for VM images instead of the default file form. The use of the iSCSI datastores presents several benefits, especially regarding performance.
It is developed to work with tgtd, the Linux SCSI target framework. However this driver is written in a way it can be easily hacked into working with specific SAN systems or other iSCSI target softwares.
There are some limitations that you have to consider, though:
iSCSIdrivers should be made persistent.
oneadminuser should belong to the
diskgroup for the KVM hypervisor. This is needed when
dynamic_ownershipis not set.
To use iSCSI drivers, you must configure the system datastore as
shared. This sytem datastore will hold only the symbolic links to the block devices, so it will not take much space. See more details on the System Datastore Guide
It will also be used to hold context images and Disks created on the fly, they will be created as regular files.
The first step to create a iSCSI datastore is to set up a template file for it. In the following table you can see the supported configuration attributes. The datastore type is set by its drivers, in this case be sure to add
TM_MAD=iscsi for the transfer mechanism, see below.
| ||The name of the datastore|
| || The DS type, use
| || Transfer drivers for the datastore, use
| || Type for the VM disks using images from this datastore. Supported values are:
| || The tgt server host. Defaults to
| || The LVM volume group name. Defaults to
| || The base IQN for iSCSI target. Defaults to
| || Starting target ID. Defaults to
| ||Paths that can not be used to register images. A space separated list of paths.|
| ||If you need to un-block a directory under one of the RESTRICTED_DIRS. A space separated list of paths.|
For example, the following examples illustrates the creation of a iSCSI datastore using a configuration file. In this case we will use the host
iscsitarget as our iSCSI target server.
> cat ds.conf NAME = production DS_MAD = iscsi TM_MAD = iscsi VG_NAME = vg-one HOST = iscsitarget > onedatastore create ds.conf ID: 100 > onedatastore list ID NAME CLUSTER IMAGES TYPE TM 0 system none 0 fs shared 1 default none 3 fs shared 100 production none 0 iscsi shared
You can check more details of the datastore by issuing the
onedatastore show command.
The iSCSI transfer driver will issue a iSCSI discover command in the target server with
iscsiadm. Once the block device is available in the host, the driver will login, mount it and link it to
The hosts must have Open-iSCSI installed, which provides
In order for
iscsiadm to work, it needs to be able to make a connection on the default iSCSI port (3260) with the iSCSI target server. Firewalls should be adjusted to allow this connection to take place.
oneadmin user must have
sudo permissions to execute
iscsiadm. Additionally, the
oneadmin user should to the
System administrators and integrators are encouraged to modify these drivers in order to integrate them with their iSCSI SAN/NAS solution. To do so, the following is a list of files that may be adapted:
iscsiadm discoverand logs in.