mbpctrefreshthresh client option

For example, when a 128 MB block of a production disk changes more than the percentage specified by the mbpctrefreshthresh option, the entire 128 MB block is copied to the IBM Storage Protect server. The block is represented as a single IBM Storage Protect object.

Before you set a value for the mbpctrefreshthresh option, review the following information:

Preferred setting

The preferred value is the default, 50. When a 128 MB megablock changes by a percentage that exceeds this value since its last refresh (a full copy to the IBM Storage Protect server), the entire megablock is refreshed.

If you are backing up to a tape storage pool on the server, you might decrease this value so that megablock refreshes occur more often. This way, the data that was backed up for each virtual machine guest disk is more likely to be collocated on tape volumes. This setting might improve restore performance in such cases.

Effects on performance

When a megablock is refreshed, the objects that were used to represent the megablock area in previous backups are expired. This option can affect the quantity of data that is copied to the IBM Storage Protect server and the server database-related processor utilization during incremental forever backups.

Potential trade-offs for this setting

Setting this option close to its maximum value of 100 can result in sending less data to the IBM Storage Protect server during an average incremental forever backup operation. However, the number of database entities that the IBM Storage Protect server must track increases. This result can increase server processor utilization during incremental forever backups by a small degree.

Setting this option close to its minimum value of 1 can result in marginal database processing savings during incremental forever backups. However, the quantity of data that is copied to the IBM Storage Protect server might be higher and might approach the size of a full backup.