Support for system recovery where OS file systems reside on one of the disks enabled with BMR supported multipath environments. This multi-path enabled disk can be either local disk or SAN Lun.

Problem

Brief introduction to multipath I/O

In disk storage terminology, a multipathed I/O is a fault-tolerance and performance boosting technique whereby there is more than one physical path between the server and its mass storage devices connected through the adaptors, controllers, ports and the connecting switches.

Example 1: A volume on SAN connected to two Fibre Channel ports
 

Example 2: A SCSI disk connected to two SCSI controllers on the same computer.

In case one adaptor, controller, port or switch fails, the operating system can route I/O through the other controller transparently to the application with no changes visible to the applications, other than may be a brief latency. Multipathing protects against the failure of paths but not from the failure of a specific storage device. Environments with multipathed systems can leverage the redundant paths to provide performance enhancing features, such as:

• Dynamic load balancing / Increased throughput
• Automatic path management
• Dynamic reconfiguration

Default Netbackup BMR support for the multipathed (MPXIO) based storage volumes:

Netbackup BMR offers "in compliance" support for MPXIO environments for some operating systems.

During a backup of a client which has "BMR known and supported" multi-pathing configuration, BMR will automatically mark the multi-pathed disk/s as "Restricted". Thus during a restore, the "restricted" disks cannot be overwritten. However it allows the administrator to map and restore the data on those "Restricted " volumes to any other local or non-multi-pathed volumes.

Example: If a client has multipathed volumes over SAN using EMC PowerPath, then BMR will mark these volumes as "Restricted" during the backup. At the time of BMR based restore, the user may recover file systems over these disk/s to either local or any other SAN attached LUNS that are not multi-path enabled.

Why does BMR mark the multipathed disks as "Restricted" in client’s BMR configuration during backup?

During backup, BMR resolves multiple paths to exact unique physical disks and captures this information within the client's "current configuration". However the recovery environment of BMR does not have multi-path software embedded (like EMC PowerPath). BMR recovery environment cannot resolve multi-pathed disks on given target hardware; hence mapping the restore time disks to original client environment may fail. Thus multi-path enabled disks are marked as "Restricted" by-default during backup time itself to avoid any recovery time failure and disk overwriting.

What exactly are the "BMR known and supported" multipathed environments?

Currently supported multi-pathed environments are:

• EMC PowerPath on Unix / Linux / Windows supported platforms
• Linux native multi-pathing (supported since Netbackup 7.5 release)

For these supported environments, BMR resolves multi-paths to exact unique physical disk at the time of backup. Also, as mentioned earlier, BMR marks them as "restricted" to prevent a recovery time disk mapping confusion.

How is a client system having operating system volumes residing over BMR supported multi-path enabled environments recovered?

As mentioned above, EMC PP and Native Linux Multi-pathing environments are supported by BMR where the multi-pathed disks are marked as "Restricted" during client BMR enabled backup. Here "Restricted" disks to BMR means those disk/s that cannot be used during recovery.

To recover client system from disaster, its OS volumes must to be restored. Follow instructions described in Solution to restore client system having its operating system volumes residing over multi-path enabled disks/s.

Solution

To restore an operating system based over an enabled multipath, complete the following steps:

This solution describes how to restore operating system based over multi-path enabled . The steps to be followed are as below.

1. Create a copy of the configuration of the desired BMR client to restore using NetBackup Administrator Console.

2. Make sure that multipath environment is disabled on the target hardware where BMR restore is intended.

3. Perform a Prepare-To-Discover operation using this copied configuration. Refer to the BMR admin guide section Discovering a configuration for details on Prepare-To-Discover operation.  (BMR Admin Guide.)

4. Upon successful PTD operation, you will see a discovered configuration under NetBackup Administrator GUI > Bare Metal Restore Management > Resources > Discovered Configurations.

5. From the command prompt, cd to the .../netbackup/bin directory and execute the following command:

# ./bmrovradm –enable “Do not auto-restrict disks” –client <client_name> -config <copied_config_name>

Note: The parameters to above command are case sensitive. You may need to repeat this command line for different clients and their configurations.

6. Edit the copied configuration from the Admin Console by right-clicking and selecting Change option.

7. Locate Volumes tab on left side menu.  Select the Initialize option.

8. Initialize this configuration with the discovered configuration. The discovered configuration should be displayed in the drop-down list of BMR configurations.

9. Select the Empty Disks option from the left-side menu and un-restrict the discovered disks.

10. Using the volume mapping GUI, map volumes onto the target discovered disks as intended.

Note: Be aware of target multipath environments and map original client multipath-based volumes onto these discovered disk(s).   Multiple entries for the same volume in the original disk view pane may be seen, but only one volume can be selected to perform its mapping to an intended target disk.

11. Save the copied configuration after completing the volume mapping process.

12. Perform a Prepare To Restore for this copied configuration.

13. Boot the target hardware for BMR restore.

Note: After a successful BMR recovery of the client system, the multi-path environment can be re-enabled on that target hardware.  Reboot the client system for the multipath environment to take effect.  In rare cases, manually enabling the multi-path environment may be required if the system does not show it post-reboot.

Applies To

NetBackup BMR 7.6.0.2 and later