FAQs - Netbackup BMR supported platforms for backup and restore to multi-pathed volumes.
|Article:TECH204180|||||Created: 2013-03-22|||||Updated: 2013-11-11|||||Article URL http://www.symantec.com/docs/TECH204180|
This article addresses some of the most frequently asked questions on supported platforms and their multi-pathed volumes (disks) using Netbackup BMR for backup and restore.
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
Does Netbackup BMR support the backup and restore to multipathed (MPXIO) 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 redirect the data on those "restriced volumes" to any other local or non-multi-pathed volumes.
For example: If a client has multipathed volumes over SAN using EMC PowerPath, then BMR will mark these volumes as "Restricted" during backup. At the time of BMR based restore, the user may recover file systems over such volumes to either local disks or any other SAN attached LUNS that are not multi-pathed.
At the time of restore I tried to un-restrict a "restricted" disk and got this error
"Unrestricting DMP disk is not supported. (Status 252)"
This is by design. Any attempt to un-restrict the "Restricted" disk will result in this error.
Why does BMR mark the multipathed disks as "Restriced" 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 identify multi-pathed disks on given target hardware. Thus it is marked as "Restricted" to avoid recovery time failure.
So, 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)
BMR supports just the above mentioned multi-pathed environment setups. 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 failure.
What if the multipathed environment happens to be different that those listed above?
At the time of backup, BMR will fail to identify unique disk names. The captured information will show multiple-disk names that were detected from the available multiple paths. They will not be marked as "restricted", thus at the time of restore there could be challenges in selectively restricting volumes before proceeding with a restore to alternate non-multipathed disk/s. Symantec technical support cannot assist in such scenarios.Customer may seek assistance from Symantec Consulting Services for a customized solution ....
More information on Symantec consulting services …
What if the system volumes are also residing on multipathed SCSI or SAN?
The overwrite restriction will prevent data restore and thus BMR will not be able to recover such systems. BMR cannot recover a server having "operating system volumes" residing on multi-pathed SCSI or SAN.
Our Solaris systems have the OS residing on SAN single path disks however all other volumes are natively SAN multipathed, which we understand is "not supported" by BMR. Can we use BMR to restore just the boot / root / system volumes that are not multipathed?
BMR can be used to restore just the local or SAN attached non-MPXIO system disks.
During the "Prepare to Restore" operation you should choose the option to "Restore system disks/volumes only"
Is there a workaround solution to restore boot / root / system volumes residing on multi-pathed disk?
Currently there is no workaround solution offered by Symantec technical support. Customers may contact Symantec consulting services for a customized solution.
Article URL http://www.symantec.com/docs/TECH204180