Optimized duplications using a different media server from that which performed the backup

Problem

It has been noticed in certain scenarios there are concerns over how NetBackup performs duplications using optimized duplication (opt-dup).  Depending on the model deployed, backups can be performed using one media server, but a duplication can use a different media server.  With opt-dup duplications the media server defined to perform the read operation has very little requirement to do any work, as the work is performed by the storage server which is associated to the disk pool, where the initial backup resides.  The media server action is to just initiate the task (much like an orchestra conductor), it's left to the storage server to send the data to the remote destination and destination disk pool.

Depending upon the NetBackup and storage server configurations, there is a possibility opt-dup duplications can fail with credential errors, *if* the backup is performed to a disk pool which only has a single media server selected, however, the destination disk pool has multiple media servers selected.  The problem occurs because resources are allocated for the destination storage unit, and if a media server selected is not a media server which has access to the disk pool where the initial backup was performed, a credential failure will appear and the duplication fails.

The fact we see a different media server listed, does not indicate this media server is sending data across the network, it’s just telling the storage server to do the work.

Additional note:- When optimized duplications are performed the ALTREADHOST and the -COMMON_SERVER_FOR_DUP options are not adhered to. This is because although another media server is registered as performing the read operation, in actual fact the opt-dup operation is still performed by the storage server associated to the original deduplication disk pool (OST plugin does the work).

Error Message

The optimized duplications fail with STATUS 2107 (NetBackup status: 2107, EMM status: Requested media server does not have credentials or is not configured for the storage server), because the READ host selected does not have credentials.

Cause

NetBackup storage server and disk pool configurations do not have the same media servers defined at both the read and write sides of the optimized duplication process.

Solution

NetBackup is working as designed and this is documented in the Veritas NetBackup 7.5 Deduplication Guide page 39, and at the time this technical article was written, there are no known plans to alter this behaviour.
 

Workaround:-  Allow the same media servers access to the storage server and disk pool which performed the initial backup, which are defined for the destination storage server and disk pool.

Applies To

NetBackup 7.5 and later revisions.