Ensure you are familiar with the small computer system
interface (SCSI) back-end support.
The SCSI back-end layer performs the following functions:
- Controls access to individual disk controller systems that are
managed by the cluster.
- Receives requests from the virtualization layer, processes them,
and then sends them to managed disks (MDisks).
- Addresses SCSI-3 commands to the disk controller systems on the
storage area network (SAN).
Disk controller systems and logical units
Disk
controller systems reside on the SAN fabric and are addressable by
one or more worldwide port names (WWPNs). A disk controller system
might contain one or more logical units (LUs), each identified by
a different logical unit number (LUN). Disk controller systems managed
by the SAN Volume Controller typically contain multiple LUs.
Logical unit (LU) access modes
LUs within
a disk controller system might be placed in one of three access modes:
- Unconfigured
- This is the default mode for all newly discovered LUs. You cannot
use these LUs for input/output (I/O) operations until you change the
mode and make it an MDisk.
- Image
- This mode enables you to directly map an LU to a virtual disk
(VDisk). An image-mode LU is an MDisk.
- Managed space
- This mode enables the virtualization function to be performed
on the LU or MDisk.