Description

When using Dynamic Multi-Pathing (DMP) as the managing multi-pathing driver, DMP can expose extended attribute characteristics for specific storage arrays. The array based attribute content is not exposed when using third-party drivers (TPD), i.e. EMC PowerPath, MPxIO and MPIO.

The DMP extended attributes or flags are discovered by the Device Discovery Layer (DDL) corresponding to a DMP LUN or Disk. These attributes identify a LUN to a specific hardware category.

The list of categories includes:
 

Each LUN can have one or more of these extended attributes. The DDL discovers the extended attributes during the device discovery activity and by using the appropriate array support library (ASL) for the specific array.
The array intelligence is written within the ASL.
 
Some arrays provide a way to dynamically change the properties of LUNs.

For example, the EMC Symmetrix array allows write-protected/write-disabled (WD|read-only), not-ready (NR) and read-write (RW) enabled LUN attribute content to be exposed to DMP.
This is possible by using the EMC specific ASL to extract disk based content from defined areas on the disk via a SCSI inquiry operation. 

As long as the disk is capable of presenting LUN specific content using SCSI inquiry commands, the array based ASL can be enhanced to expose such value add content.
 

In most cases, you must completely offline|stop using the device before the device can reflect the changed characteristics of the LUN.


To enable Veritas Volume Manager (VxVM) in connection with DMP to make such LUN characteristics available and consistent, specific steps are required.
 

We recommend taking the device offline before detecting changed LUN properties. Once the LUN attributes have changed to the required state, the device can then be brought back online again.

 
Steps
 

1.] # vxdisk offline

2.] Perform array activity

3.] # vxdisk online


Intelligent LUNs


In certain cases, such device types as EMC BCV (Hardware Clone) and SRDF (Hardware Replicated) can remain online as DMP is fully aware of the LUN characteristics via the intelligence provided via the EMC ASL.
The DMP extended attribute content can be displayed in many ways for such intelligent storage arrays using the VxVM "vxdisk -e list" CLI command, and in later versions using the "vxdisk -px LIST_CLONE list" command.

With such intelligent device types, the DMP extended attribute may still require a manual refresh using the VxVM "vxdisk scandisks" CLI command. 
Once the device status reflects the required state, DMP should be manually updated with the new LUN details to ensure the appropriate VxVM command outputs do reflect the current LUN characteristics.

Steps
 

1.] The H/W Clone/Replicate device state is being intentionally modified/changed.

2.] The H/W related activity i s complete .

3.] Refresh VxVM and DMP extended attribute content.

# vxdisk scandisks
 

In a clustered environment, the manual refresh of the extended attributes needs to be performed across all nodes in the cluster.


Recommendation: VxVM product releases 6.0.5 and 6.1.1 (MR1) or higher should be deployed where possible to benefit from additional functionality enhancements.

Example:

For AIX deployments, a minimum of 6.0.5 must be installed for VxVM to correctly detect H/W device states changes. See attached articles for more product specific information.

 

Advanced Reporting


The capability of showing the special LUN type properties with VxVM is called “Advanced Reporting”.

For a list of ASLs that support extended attributes, and descriptions of these attributes, refer to the hardware compatibility list (HCL).

The HCL will have a link to the ASLAPM ( Enabled Arrays - Information regarding the Array Support Libraries and Array Policy Modules, included in the VRTSaslapm package) related articles outlining which LUN properties (extended attributes) can be reported by VxVM.