The mbobjrefreshthresh (megablock object refresh threshold) option is a number defining a threshold. When the number of Tivoli® Storage Manager objects that are needed to describe any 128 MB megablock exceeds this value, the entire megablock is refreshed and the objects that were used to represent this area, in previous backups, are expired.
During a backup operation, VMware virtual machine data is stored on the Tivoli Storage Manager server in 128 MB units, called megablocks. If an area on the production disk changes and a new incremental backup is performed, a new megablock is created to represent the changes that were made to the previously backed up data. Because a new megablock can be created with each incremental backup, eventually the megablocks can adversely affect the performance of the Tivoli Storage Manager database, and therefore, adversely affect the performance of most Tivoli Storage Manager operations.
Use this option when estimating Tivoli Storage Manager objects that represent production data for each virtual machine backup. For example, when the number of Tivoli Storage Manager objects exceed this value, the megablock is refreshed. This action means that the entire 128-MB block is copied to the Tivoli Storage Manager server and is represented as a single Tivoli Storage Manager object. The minimum value is 2 and the maximum value is 8192. The default value is 50.
Supported clients
This option is valid for clients that are data mover nodes that protect VMware virtual machines.
Options file
Specify this option in the client options file.
Parameters
The minimum value you can specify is 2 megablocks, the largest value is 8192 megablocks; the default is 50 megablocks.
Examples
Set this option to trigger a megablock refresh when the number of objects needed to represent an updated megablock exceeds 20 objects:MBOBJREFRESHTHRESH 20Related information
Additional information about using the MBOBJREFRESHTHRESH option for optimal database performance is described in Incremental forever strategy.