Third-party driver coexistence


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Third-party driver coexistence

The third-party driver (TPD) coexistence feature of VxVM 4.1 allows I/O that is controlled by third-party multipathing drivers to bypass DMP while retaining the monitoring capabilities of DMP. Provided that a suitable ASL is available, devices that use TPDs can be discovered without requiring you to set up a specification file, or to run a special command. In previous releases, VxVM only supported TPD coexistence if the code of the third-party driver was intrusively modified. The new TPD coexistence feature maintains backward compatibility with such methods, but it also permits coexistence without require any change in a third-party multipathing driver.

See "Displaying information about TPD-controlled devices" on page 131.

Autodiscovery of EMC Symmetrix arrays

In VxVM 4.0, there were two possible ways to configure EMC Symmetrix arrays:

With EMC PowerPath installed, EMC Symmetrix arrays could be configured as foreign devices as described in Foreign devices.
Without EMC PowerPath installed, DMP could be used to perform multipathing.

On upgrading a system to VxVM 4.1 or later release, existing EMC PowerPath devices can be discovered by DDL, and configured into DMP as autoconfigured disks with DMP nodes, even if PowerPath is being used to perform multipathing. There is no need to configure such arrays as foreign devices.

Scenarios for using DMP with PowerPath shows the scenarios for using DMP with PowerPath.

Scenarios for using DMP with PowerPath

PowerPath	DMP	Array mode
Installed	The `libvxemc` ASL handles EMC arrays and DGC claiming internally. PowerPath handles failover. There is n o need to install the Cx600 ASL or APM.	Explicit failover.
Not installed; the array is not Cx600	DMP handles multipathing. The `libvxemc` ASL handles the EMC Symmetrix array.	Any.
Not installed; the array is Cx600	DMP handles multipathing. The Cx600 ASL and APM must be installed.	Any.

PowerPath

DMP

Array mode

Installed

The libvxemc ASL handles EMC arrays and DGC claiming internally. PowerPath handles failover.

There is n o need to install the Cx600 ASL or APM.

Explicit failover.

Not installed; the array is not Cx600

DMP handles multipathing.

The libvxemc ASL handles the EMC Symmetrix array.

Any.

Not installed; the array is Cx600

DMP handles multipathing.

The Cx600 ASL and APM must be installed.

Any.

If any EMCpower discs are configured as foreign discs, use the vxddladm rmforeign command to remove the foreign definitions, as shown in this example:

# vxddladm rmforeign blockpath=/dev/emcpower10 \

charpath=/dev/emcpower10

To allow DMP to receive correct enquiry data, the Common Serial Number (C-bit) Symmetrix Director parameter must be set to enabled.


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