That is normal for mailbox backups due to the process involved. Do you really HAVE to backup mailboxes? Read up on Recovery Storage Group to restore an Information Store from where individual items can be restored.
See this TechNote:
http://seer.entsupport.symantec.com/docs/280826.htm
If file system backups from the Exchange client are running at a satisfactory speed, then most likely there is no performance tuning within NetBackup which will improve the speed of mailbox backups. There are two general ways to perform baseline testing of Exchange Mailbox backup throughput for the purpose of determining the theoretical maximum possible throughput for mailbox backups:
1. The
exmerge utility from Microsoft is used to extract the data directly out of the database into a
.pst file. The utility should be used to export a few larger mailboxes, and the performance on these mailboxes can be used to gauge the time it should take to complete the backup process. The utility does create a log file which can be viewed after the process has run to gauge the amount of time the process took. Since this is a Microsoft utility, refer to this Microsoft link for operating instructions:
http://support.microsoft.com/?kbid=174197
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Note: Several factors can impact mailbox backup performance:
- The creation of more message items in the database creates more data to back up, along with more fragmentation in the database, decreasing access time.
- Running an antivirus scanner in On-Access/VAPI mode causes a scan of every item backed up and significantly degrades the process.
- Database defragmentation running at the same time as the mailbox backup degrades the performance.
- Very large mailboxes with many message items have increased initial scan times and slow backup performance.