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.

 

 

The Device Discovery Layer (DDL) allows dynamic addition of disk arrays. DDL
discovers disks and their attributes that are required for VxVM operations.

The DDL is administered using the vxddladm utility to perform the following tasks:
■ List the hierarchy of all the devices discovered by DDL including iSCSI devices.
■ List all the Host Bus Adapters including iSCSI
■ List the ports configured on a Host Bus Adapter
■ List the targets configured from a Host Bus Adapter
■ List the devices configured from a Host Bus Adapter
■ Get or set the iSCSI operational parameters
■ List the types of arrays that are supported.
■ Add support for an array to DDL.
■ Remove support for an array from DDL.
■ List information about excluded disk arrays.
■ List disks that are supported in the DISKS (JBOD) category.
■ Add disks from different vendors to the DISKS category.
■ Remove disks from the DISKS category.
■ Add disks as foreign devices

 

If you try to reprovision a LUN or set of LUNs whose previously-valid operating
system device entries are not cleaned up, the following messages are displayed.
Also, DMP reconfiguration during the DMP device scan and DMP reconfiguration
are temporarily inhibited.
See “Cleaning up the operating system device tree after removing LUNs”on page 220.
VxVM vxdisk ERROR V-5-1-14519 Data Corruption Protection Activated- User Corrective Action Needed
VxVM vxdisk INFO V-5-1-14521 To recover, first ensure that the OSdevice tree is up to date (requires OS specific commands).
VxVM vxdisk INFO V-5-1-14520 Then, execute 'vxdisk rm' on thefollowing devices before reinitiating device discovery.

The message above indicates that a new LUN is trying to reuse the target ID of an older LUN. The device entries have not been cleaned, so the new LUN cannotuse the target ID. Until the operating system device tree is cleaned up, DMP prevents this operation.