Selection of storage units: performance considerations
Many different NetBackup mechanisms write backup images to storage devices, such as: backup policies, storage lifecycle policies (SLPs), staging storage units, Vault duplication, and ad hoc (manual) duplication. When writing a backup image to storage, you can tell NetBackup how to select a storage unit or let NetBackup choose the storage unit.
There are three ways to specify destination for backups and duplications:
Storage unit (the preferred way)
Storage Unit Group (slower than storage units)
If tape storage unit groups are used, limit the number of storage units in a storage unit group to 5 or less.
Note:
Use of storage unit groups is not recommended with MSDP pools. It is recommended to specify a specific set of clients or specific workload to a consistent and specific MSDP pool. This optimizes capacity and deduplication efficacy.
Any Available.
Use only in test environments.
Although Storage Unit is the preferred method for most large environments, the following sections, Performance considerations for the Any Available method and Performance considerations for the Storage Unit Groups method discuss the pros and cons of specifying a storage unit group versus allowing NetBackup to choose from a group (Any Available).
Note:
The more narrowly defined the storage unit designation is, the faster NetBackup can assign a storage unit, and the sooner the job starts.
As a rule, the Any Available method should only be used in small, simple environments.
For most backup operations, the default is to let NetBackup choose the storage unit (a storage destination of Any Available). Any Available may work well in small configurations that include relatively few storage units and media servers.
However, Any Available is NOT recommended for the following:
Configurations with many storage units and media servers. Any Available is not recommended.
Configurations with disk technologies (such as AdvancedDisk, PureDisk, OpenStorage). With these newer disk technologies, Any Available causes NetBackup to analyze all options to choose the best one available. Any Available is not recommended.
In general, if the configuration includes many storage units, many volumes within many disk pools, and many media servers, note: the deep analysis that Any Available requires can delay job initiation when many jobs (backup or duplication) are requested during busy periods of the day. Instead, specify a particular storage unit, or narrow NetBackup's search by means of storage unit groups (depending on how storage units and groups are defined).
For more details on Any Available, see the NetBackup Administrator's Guide, Volume I.
In addition, note the following about Any Available:
For Any Available, NetBackup operates in prioritized mode, as described in the next section. NetBackup selects the first available storage unit in the order in which they were originally defined.
Do not specify Any Available for multiple copies (Inline Copy) from a backup or from any method of duplication. The methods of duplication include Vault, staging disk storage units, lifecycle policies, or manual duplication through the Administration Console or command line. Instead, specify a particular storage unit.
Although Storage Unit is the preferred method for most large environments, a Storage Unit Group may be useful. It contains a specific list of storage units for NetBackup to choose from. Only these storage units are candidates for the job.
You can configure a storage unit group to choose a storage unit in any of the following ways:
Prioritized
Choose the first storage unit in the list that is not busy, down, or out of media.
Choose the first storage unit in the list that is not down or out of media.
Round robin
Choose the storage unit that is the least recently selected.
Media server load balancing
NetBackup avoids sending jobs to busy media servers. This option is not available for the storage unit groups that contain a BasicDisk storage unit.
You can use the New or Change Storage Unit Group dialog in the NetBackup Administration Console to make the desired modifications. NetBackup gives preference to a storage unit that a local media server can access. For more information, see the NetBackup online Help for storage unit groups, and the NetBackup Administrator's Guide, Volume I.
Note:
Regarding storage unit groups: the more narrowly defined your storage units and storage unit groups, the sooner NetBackup can select a resource to start a job.
In complex environments with large numbers of jobs required, the following are good choices:
Fewer storage units per storage unit group.
Fewer media servers per storage unit. In the storage unit, avoid Any Available media server when drives are shared among multiple media servers.
Fewer disk volumes in a disk pool.
Fewer concurrent jobs. For example, less multiplexing, or fewer tape drives in each storage unit.
See NetBackup job delays.