3.2.3 iSCSI Storage Attached Network

With Internet SCSI, or iSCSI, you can connect storage entities to client machines, making the disks behave as if they are locally attached disks. iSCSI enables this connectivity by transferring SCSI commands over existing IP networks between what is called an initiator (the client) and a target (the storage provider).

To establish a link with iSCSI SANs, all Oracle VM Servers can use configured network interfaces as iSCSI initiators. It is the user's responsibility to:

  • Configure the disk volumes (iSCSI LUNs) offered by the storage servers.

  • Discover the iSCSI storage through Oracle VM Manager. When discovered, unmanaged iSCSI and Fibre Channel storage is not allocated a name in Oracle VM Manager. Use the ID allocated to the storage to reference unmanaged storage devices in the Oracle VM Manager Web Interface or the Oracle VM Manager Command Line Interface.

  • Set up access groups, which are groups of iSCSI initiators, through Oracle VM Manager, in order to determine which LUNs are available to which Oracle VM Servers.

Performance-wise, an iSCSI SAN is better than file-based storage like NFS and it is often comparable to direct local disk access. Because iSCSI storage is attached from a remote server, it is perfectly suited for an x86-based clustered server pool configuration where high availability of storage and the possibility to live migrate virtual machines are important factors.

In SPARC-based environments, iSCSI LUNs are treated as local disks. Since OCFS2 is not supported under SPARC, these disks cannot be used to host a server pool cluster file system and they cannot be used to host a repository. Typically, if iSCSI is used in a SPARC environment, the LUNs are made available directly to virtual machines for storage.

Provisioning of iSCSI storage can be done through open source target creation software at no additional cost, with dedicated high-end hardware, or with anything in between. The generic iSCSI Oracle VM Storage Connect plug-in allows Oracle VM to use virtually all iSCSI storage providers. In addition, vendor-specific Oracle VM Storage Connect plug-ins exist for certain types of dedicated iSCSI storage hardware, allowing Oracle VM Manager to access additional interactive functionality otherwise only available through the management software of the storage provider. Examples are creating and deleting LUNs, extending existing LUNs and so on. Check with your storage hardware supplier if a Oracle VM Storage Connect plug-in is available. For installation and usage instructions, consult your supplier's plug-in documentation.

Oracle VM is designed to take advantage of Oracle VM Storage Connect plug-ins to perform LUN management tasks. On a storage array do not unmap a LUN and then remap it to a different LUN ID without rebooting the affected Oracle VM Servers. In general, remapping LUNs is risky because it can cause data corruption since the targets have been switched outside of the affected Oracle VM Servers. If you attempt to remap a LUN to a different ID, affected Oracle VM Servers are no longer able to access the disk until they are rebooted and the following error may appear in /var/log/messages:

Warning! Received an indication that the LUN assignments on this target have changed. 
The Linux SCSI layer does not automatically remap LUN assignments.