iSCSI Plug-in

iSCSI-based filesystem images support

The iSCSI-plugin adds support to the openQRM server to boot nodes from iSCSI-targets. This mechanism is quite different from the use of nfs/nfsroot because iSCSI is a kind of "remote block device" and not a directory-based network-filesystem.  This block device is a "normal" ext2/3/reiserfs filesystem which can be mounted for use by the nodes.

About the iSCSI-target (server)

• Available targets
• Commercial : Ardis, Netapp, Fibrecat, Snap Server, rapidSAN-iS
  
• Open-source: Enterprise iscsi target project, uhn-iscsi (please check the urls below in the "Urls" section)
  

Note:  The iSCSI-targets are serving "real" hard disks or block device files (e.g. the enterprise iSCSI target).  The iSCSI-disks/files have a partition table and a "common" linux filesystem e.g. ext3, reiserfs,  gfs, etc.

Specific ISCSI-target handling for the QRM-server

You will need to download and install one of the above listed iSCSI targets and configure and start it on one of the systems in your network.


About the ISCSI-initiator (client)

The ISCSI-initiator has 2 parts :

1. the ISCSI-initiator kernel module
   
2. the ISCSI-daemon

When the ISCSI-initiator is started (how depends on the implementation) it
"discovers" all existing ISCSI-LUN's according to its configuration.

Here a detailed flow of the discovery procedure :

• On the client the iscsi-module is inserted into the kernel with insmod
• It starts the iscsid-daemon to communicate with the iscsi-module
• The iscsid dameon reads the configuration file and logs in to the target
  
• The targets acknowledges the login
• The client sends a "discover" request to the target
  
• The target replies with the configured LUN's

Specific handling for the QRM-nodes running ISCSI-filesystem images

During boot-up the linuxrc in the intird will insmod the iscsi module, create the iscsi-config file and startup the iscsid.
This causes the resource (or the iscsid daemon running on the node) to discover the ISCSI-targets LUN's according to its configuration.  It then sees the ISCSI-target LUN's as the next free scsi-device (e.g. /dev/sdb) and mounts it as the root filesystem. Then the system starts its initialization and starts as usual. 

Kernel support

There are a few dependencies for the ISCSI-initiator in the linux kernel:

• The boot-image needs to have an iscsi-modules fitting to the kernel-version on the initrd
• The boot-image needs to have an iscsid-daemon fitting to the iscsi-version on the initrd
• There are different ISCSI-initiator versions for 2.4 and 2.6 based linux kernels.

openQRM comes with two kernels, one from each of the 2.4 and 2.6 streams with iscsi support. These kernels are compiled during the openQRM-server build process. The kernels are the vanilla sources plus the specific iscsi-module and daemon that fits the kernel version.

• old/stable -> for kernel version 2.4 [1]
• new/unstable -> for kernel version 2.6 [2]

Image configuration

To use filesystem images on an iSCSI-target some configuration parameters must be added to the openQRM configuration file $QRM_BASEDIR/etc/qrm.ini.

Parameters to be added:

• iSCSI-storage-type
• iSCSI-target parameters are configured in the storage-server section.
• iSCSI filesystem-configuration parameters need to be added
• The "Environment Variables" text-box (please see also "iSCSI-tips" in the GUI)
  

For Example:

ISCSI_TARGET_NAME=node4

ISCSI_ROOT_PARTITION=1

The number of the root-partition on the ISCSI-device to connect to

ISCSI_LUN=0

The LUN on the ISCSI-target to connect

ISCSI_ROOT_FS_TYPE=ext3

The filesystem type on the ISCSI-device

ISCSI_PORT=3260

The ISCSI-target port to connect

ISCSI_HBA=0

The ISCSI-HBA to connect

ISCSI_INITIATOR=iqn.1987-05.com.cisco:01.fca433984997

The ISCSI-initiator name to authenticate with the ISCSI-target

Image creation

For information on image creation, please see this document.

RedHat

The following RedHat distributions have iSCSI support:

• Advanced Server 3.0 Update 4 and up
• Advanced Server 4.0 Update 2

The following RPM is needed:

•  iscsi-initiator-utils
  

Reference URLs

ISCSI-Targets

• [3] Enterprise Iscsi-target
• [4] Ardis Iscsi-target
• [5] Unh-Iscsi project (target and initiator)
  

ISCSI-Initiators

• [6] Iscsi-project
• [7] Open-iscsi project