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Article: 100021431
Last Published: 2023-09-01
Ratings: 0 0
Product(s): NetBackup
Problem
How does MDS select a volume from disk pool when a backup job is initiated?Solution
The volume list for a disk pool is sorted by descending values for:
FreeSpace+ Potential Freespace - Committed Space
These space values are defined as follows
Freespace is updated periodically by resource monitor, which collects this information via nbrmms on media server.
Committedspace is updated at the same time by resource monitor and represents bytes allocated for currently running backups. Please note that it is only updated if for currently running backup policies were run previously and hence have size history from previous backups.
PotentialFreespace is updated periodically by nbstserv and represents the number of bytes used by images that have had all copies made for them by a StorageLifecycle Policy and hence eligible for expiration.
The idea here is that
1. The volume with the most available space is used for each backup
2. The space values are updated periodically by asynchronous processes.
In the current design, there has never been a guarantee or an attempt to guarantee that successive jobs run on different disk volumes. That being said, for a disk pool with identically sized volumes, if they all start out empty, it is possible to see jobs that start in succession go to different volumes dependent on the update times of the capacity measurements in for the volumes and the estimated sizes of jobs using the volumes (if estimates are available).
There is an enhancement request in place to consider throttling number of concurrent jobs per volume. This will make the user to decide how many jobs can be send to a given disk volume based on the backend performance (file system, volume managerand physical lun).
References
Etrack : 1739942
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