Multistream backup is a NetBackup feature that allows multiple backups
(streams) of a single client to occur simultaneously to one or more DSUs. This feature allows clients with large amounts of data to meet a given backup window which would not be met if the data was backed up serially.
The NearStore system to which these streams are being directed has a limit on
the maximum number of simultaneous streams allowed at a time. For example,
the FAS6070 has a limit of 128 simultaneous streams.
SnapVault for NetBackup
supports multistream backups using the File System Export mode; however,
maintaining such multistream backups is difficult.
Attention: You should not implement
multistreaming backup configurations because of this difficulty. You should consult with your NetApp representative to determine the
optimal number of multistream backups for your system.
NetBackup creates a stream for each data path in the backup selection list for a policy. NetBackup tags each stream by the order of the backup selections in the policy. A backup selection at the top of the list is tagged differently from the same backup selection at the bottom of the list. Shifting location in the backup selection list for a policy is a shift of context. If the backup selection list is reordered, the context is changed for the reordered backup selections. A context change means loss of extra storage requirement for the backups.
You can use the following guidelines to ensure that the ordering of backup selections is maintained to provide a consistent context for context-based deduplication:
- Do not alter the sequence of the backup selections in a policy.
- Do not delete any backup selection from the list if it was part of a previous
backup operation.
- Only append new paths to the end of the backup selection list.
- Do not use ALL_LOCAL_DRIVES as a backup selection because the directive
maps to all drives on the local host.
Any change in the drive letter
assignment due to mapping or unmapping of network drives, results in
behavior similar to data set rename.
- Do not use wildcards in the data selection list. If NetBackup sends one stream per wildcard expansion and the
number of wildcard expansions changes between consecutive backups, this results in a change in backup context
and behavior similar to adding or deleting a data set in the middle of the backup selection list.
