Veritas Volume Manager 5.1 SP1 Administrator"s Guide (5900-1506, April 2011)

Device discovery
Device discovery is the term used to describe the process of discovering the disks
that are attached to a host. This feature is important for DMP because it needs to
support a growing number of disk arrays from a number of vendors. In conjunction
with the ability to discover the devices attached to a host, the Device Discovery
service enables you to add support dynamically for new disk arrays. This operation,
which uses a facility called the Device Discovery Layer (DDL), is achieved without
the need for a reboot.
This means that you can dynamically add a new disk array to a host, and run a
command which scans the operating system’s device tree for all the attached disk
devices, and reconfigures DMP with the new device database.
See “How to administer the Device Discovery Layer” on page 87.
About enclosure-based naming
Enclosure-based naming provides an alternative to operating system-based device
naming. This allows disk devices to be named for enclosures rather than for the
controllers through which they are accessed. In a Storage Area Network (SAN)
that uses Fibre Channel switches, information about disk location provided by
the operating system may not correctly indicate the physical location of the disks.
For example, c#t#d# naming assigns controller-based device names to disks in
separate enclosures that are connected to the same host controller.
Enclosure-based naming allows VxVM to access enclosures as separate physical
entities. By configuring redundant copies of your data on separate enclosures,
you can safeguard against failure of one or more enclosures.
Figure 1-3 shows a typical SAN environment where host controllers are connected
to multiple enclosures through a Fibre Channel switch.
Understanding Veritas Volume Manager
How VxVM handles storage management
24