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GridStor® (Alternate Data Paths) - Advanced

Table of Contents

Defining the Criteria for Using Alternate Data Paths

A storage policy can be configured to use an alternate data path using the following options:

  • When resources are busy or offline - use this option to configure your system to use an alternate data path when resources are busy or offline.
  • Load balance between the data paths - use this option to evenly distribute data protection operations amongst drive-pools, thereby not overloading a specific drive-pool.
  • LAN-free preferred data path - use this option to automatically perform LAN-free data protection operations.

When Resources Are Offline or Busy

When this option is selected the system automatically uses an alternate data path when resources are offline or busy.

When Resources Are Offline

When this option is selected, the storage policy uses an alternate data path when one of the following resources is broken or not available (and therefore marked offline by the user or by the MediaAgent):

  • MediaAgent
  • Library
  • Master Drive Pool
  • Drive Pool
  • All the drives in the Drive Pool
  • No spare media in the scratch pool associated with the copy

When Resources Are Busy

When this option is selected, the storage policy uses an alternate data path when all the drives in the library are busy.

  • All data paths are available if you select When Resources Are Offline or Busy.
  • MediaAgents must have proper connectivity to each other, so that the index can be pulled when required.

Configuring Alternate Data Path for Storage Policy Copy when Resources Are Offline or Busy

Use these steps to use an alternate data path for a storage policy copy when resources are offline or busy:

  1. From the CommCell Browser, expand Policies > Storage Policies > storage_policy.
  2. Right-click the storage_policy_copy > Properties.
  3. Click the Data Path Configuration tab.
  4. If you select Use Alternate Data Paths, alternate data paths will be used when resources are busy or offline.
  5. Select When Resources are Offline to force the storage policy copy to use an alternate data path when resources are offline.

    Tip: Resources are MediaAgent, Library, Master Drive Pool, Drive Pool, Drives in the drive pool and spare media in the scratch pool associated with this data path.

  6. Select the When Resources are Busy checkbox, to indicate that the storage policy copy must use an alternate data path when resources are busy.

    Tip: Resources are all the drives in the library attached to the preferred MediaAgent.

  7. Click OK.

Round Robin between Data Paths

When this option is selected the system automatically performs load-balancing between the resources (drives in a library or writers in a disk library) available in all the data paths. Keep in mind that the load-balancing is performed at the drive-pool level as opposed to the MediaAgent level.

The following section illustrates the load balancing operation:

If you have defined 5 data paths with 15 resources, and have 25 data protection operations running concurrently at a given time, load balancing would cause the following to occur:

  • The first operation will be performed on the default data path.
  • The second and subsequent operations are performed on the next data paths, in the order in which they were added, on the Data Paths tab of the Copy Properties dialog box.
  • Once the first five operations reserve the resources, the sixth operation is routed to another resource in the default data path, if one is available. Subsequent operations are routed to the next data path, in the order in which they were added on the Data Paths tab of the Copy Properties dialog box, until all resources are occupied.
  • Once all resources are being used, the system checks repeatedly for an available resource. When one becomes available, the next job in the queue is routed to that resource.

See Load Balancing Using Spill and Fill for information on balancing operations between available storage resources in the CommCell group.

Use these steps to use an alternate data path for a storage policy copy to configure Round-Robin between data paths:

  1. From the CommCell Browser, expand Policies > Storage Policies > storage_policy.
  2. Right-click the storage_policy_copy > Properties.
  3. On the Data Path Configuration tab, select Round-Robin between Data Paths to automatically fail over between the available data paths.
  4. Click OK.

Use Preferred Data Path

When this option is selected, the system automatically performs LAN-free backups when possible. All available MediaAgents are available as an alternate data path.

Note that although the Use preferred data path option is selected, the LAN-free Auxiliary Copy operations on the copy is not performed until the alternate data paths are selected.

Use the following steps to use preferred data path:

  1. From the CommCell Browser, expand Policies > Storage Policies > storage_policy.
  2. Right-click the storage_policy_copy > Properties.
  3. On the Data Path Configuration tab, select Use preferred data path to automatically perform LAN-free backups when possible.
  4. Click OK.

Configuring Alternate Data Paths for Primary Copies

If a storage policy is created during the library configuration process, a default data path is created for the primary copy using the MediaAgent, Library, Drive Pool and default scratch pool combination for drive pools configured within the library. If you create a new storage policy, you must specify a Library, MediaAgent, Drive and Scratch pool combination for the primary copy.

Add Data Paths to Primary Copies

Additional data paths for the primary copy can be defined from the Data Paths tab of the Copy Properties dialog box.

Use these steps to add a data path to a storage policy primary copy:

  1. From the CommCell Browser, expand Policies > Storage Policies > storage_policy.
  2. Right-click the storage_policy_copy > Properties.
  3. In the Copy Properties dialog box, click the Data Paths tab, then click Add.
  4. Select the data path candidates that you wish to add.

    Note: To add an additional data path, make sure that the existing MediaAgent in the Datapaths tab has access to (or is shared with) a new library that you wish to add.

    You can select multiple candidates by holding down the CTRL key and clicking on each of the data path candidates that you want to select.

    For copies that use a Global Deduplication Policy the Data Path must be added from the primary copy of the Global Deduplication Policy.
  5. Click OK.
  6.  Click OK to save the information in the Copy Properties dialog box.

Set the Default Data Path

After defining additional data paths, if necessary, you can set any of the data paths as the default data path for the storage policy copy.

Use the following steps to set a data path as the default data path from a storage policy copy:

  1. From the CommCell Browser, expand Policies > Storage Policies > storage_policy.
  2. Right-click the <Storage Policy Copy> and click Properties.
  3. Click the Data Paths tab.
  4. Select the data path you wish to set as the preferred data path from the list.
  5. Click Set Default. The data path is set as the default data path.

    Notice the tick mark in the icon displayed in the Status column.

  6. Click OK.

Configuring Alternate Data Paths for Secondary Copies

Data paths can be added to secondary copies to enable LAN free Auxiliary Copy operations, so that network resources can be freed wherever possible.

Add Data Paths to Secondary Copies

When a secondary copy is created, you must select the default data path for the copy by selecting the MediaAgent, Library, Drive Pool and scratch pool combination. This data path will be used to access the secondary copy when an Auxiliary Copy operation is performed.

However you can add data paths for the secondary copy so that any Auxiliary Copy operations can be performed using a LAN-free data path.

As with the primary copy, additional data paths for the secondary copy can also be defined from the Data Paths tab of the Copy Properties dialog box.

When you add the data path for the secondary copy it is sufficient to add one path per MediaAgent-Library combination. The system automatically uses an available data path to perform LAN free Auxiliary Copy operations. Keep in mind, that when you add data paths in the secondary copies, the system automatically tries to perform a LAN-free read operation. (This is opposed to the primary copies, where the system strives to perform both the read and write operations when the LAN-free option is selected.)

Use the following steps to add a data path to a storage policy secondary copy:

  1. From the CommCell Browser, expand Policies | Storage Policies | storage policy.
  2. Right-click the appropriate storage policy copy and click Properties.
  3. On the Copy Properties dialog box, click the Data Paths tab and then click Add.
  4. Select the data path candidates that you wish to add.

    Note: To add an additional data path, make sure that the existing MediaAgent in the Datapaths tab has access to (or is shared with) the new library that you wish to add.

    You can select multiple candidates by holding down the CTRL key and clicking on each of the data path candidates that you want to select.

    For copies that use a Global Deduplication Policy the Data Path must be added from the primary copy of the Global Deduplication Policy.
  5. Click OK repeatedly until all dialog boxes are closed.

See Although common data paths are defined in primary and secondary copies, another data path is being used for Auxiliary Copy operations for information about alternate data path being used by Auxiliary Copy operations.

Configuring Alternate Data Paths for Subclients

Subclient data paths are supported by all agents that require an iDataAgent Backup Storage Policy. If necessary, different data path subsets can be selected for database agents that use different storage policies for data and log files.

Each subclient can be configured with a subset of data paths from the data paths available in the storage policy associated with the subclient . The following options are provided while defining the data paths for a subclient:

  • Facility to select a subset of data paths from the list of available data paths.
  • Facility to assign a priority for the selected data paths.
  • If necessary, facility to override the default data path on storage policy and use the other data path from the subset of data paths available for the subclient.

    The Override Datapaths option is not supported if the subclient is associated with an Incremental Storage Policy.

    The data paths and the priority established at the subclient level takes precedence over the data paths defined at the storage policy copy.

When a secondary (storage policy) copy is promoted as the primary copy, the data paths defined in the secondary copy is automatically used by the subclient. If necessary, you must establish the default data path and set the priority once the secondary copy is promoted.

Subclient data paths are not supported by Subclient Policies and cannot be configured using the Command Line interface. When a data path is deleted from the storage policy (or a library is deconfigured) the data path is automatically removed from the subclient.

Add Data Paths to a Subclient

By default, the system uses the data path associations defined in the primary copy of the storage policy to perform data protection operations. However, you can perform the following operations also:

  • Select a subset of the available data paths for the subclient.
  • Set a priority for the selected data paths.

Use the following steps to configure data paths for subclients:

  1. From the CommCell Browser, expand Client Computers | client | File System | defaultBackupSet.
  2. Right click the appropriate subclient and click Properties.
  3. On the Subclient Properties dialog box, click the Storage Device tab and then click the Data Paths.
  4. Select the Override Data Paths check box to define the necessary data paths at the subclient level.
  5. Click OK.

Assign Priorities for Subclient Data Paths

Use the following steps to assign priorities for subclient data paths:

  1. From the CommCell Browser, expand Client Computers | <Client> | File System | defaultBackupSet.
  2. Right click the <Subclient> and click Properties.
  3. Click the Storage Device tab.
  4. Click the Data Paths.
  5. Select the Override Data Paths check box to define the necessary data paths at the subclient level.
  6. Select the Use check box to assign priority to the data path for the subclient.
  7. Click Priority and type a number as priority.
  8. Click the Refresh Priority to sort the display based on the established priority.
  9. Click OK.

Configuring Multiple Data Paths for a Storage Policy Copy

Use the following steps to configure multiple data paths for a storage policy copy:

  1. From the CommCell Browser, expand Policies | Storage Policies | storage policy.
  2. Right-click the appropriate storage policy copy and click Properties.
  3. Click the Data Path Configuration tab.
  4. Select the criteria under which a storage policy copy must use an alternate data path.
    • Select Use Alternate Data Paths to indicate that alternate data paths must be used only when resources are busy and/or resources are offline.
    • Select Round-Robin between Data Paths to automatically fail over between all the available data paths.
    • Select Use preferred data path to automatically perform LAN-free backups, wherever possible.
  5. Add the data paths to the storage policy copies for which you wish to add multiple data paths.

The storage policy copy will automatically switch to an alternate data path, when the preferred data path is either offline or busy, as established in the criteria for using an alternate data path.

Setting the Number of Streams for Alternate Data Paths

When you add or delete an alternate data path, you must reset the number of streams that are defined for the Storage Policy.

The maximum number of streams for a storage policy, with a primary copy that has alternate data paths should be equal to the sum of all unique drives associated with the drive pools and/or the sum of all writers in the mount paths associated with disk libraries in all alternate data paths. Consider the following scenarios, when the maximum number of streams defined is either too many or too little, when you have specified the criteria to use alternate data paths when resources are busy:

  • If the maximum number of streams in a Storage Policy is less than the sum of drives/writers in mount paths associated with all the data paths in a primary copy, then all the resources (drives/writers in mount paths) available in the data paths will not be utilized. For example, if the sum of drives/writers in mount paths in all the data paths is 20, and you have specified 10 as the maximum number of streams, at any given time, only 10 jobs would succeed and the remaining jobs would go into the Waiting status with the Job Delay Reason stating that no resources are available for the job. In such a situation to fully utilize all the available resources, the maximum number of streams should be set to 20.
  • If the maximum number of streams in a Storage Policy is more than the sum of drives/writers in mount paths associated with all the data paths in a primary copy, only as many jobs as the total number of available drives will succeed. For example, if the sum of drives/writers in mount paths in all the data paths is 20, and you have specified 30 as the maximum number of streams, at any given time, only 20 jobs would succeed and the remaining jobs would go into the Waiting status with the Job Delay Reason stating that no resources are available for the job.

You can specify the number of streams available to perform backup or restore operations for all the subclients which use the storage policy. The number of data streams is the same for all the copies in the storage policy. You cannot change the number of data streams for individual copies.

Follow the steps given below to specify the number of streams:

  1. From the CommCell Browser, expand Policies | Storage Policies.
  2. Right-click the appropriate storage policy and click Properties.
  3. In the Device Streams box, enter the number of available streams.
  4. Click OK.

    You can change the number of data streams only if any backup data is not associated with the storage policy. If a subclient associated with a storage policy is configured to use multiple streams, the number of streams for the storage policy must be greater than or equal to number of streams defined for the subclient.

Performing Data Path Configurations from the Command Line Interface

You can modify several data path options from the command line interface. For more information, see Specify Conditions for Using an Alternate Data Path.

Deleting a Data Path from a Storage Policy Copy

You cannot delete a data path that is set as the default data path.

You can delete a data path when the associated storage policy is reserved for data protection operations.

Use the following steps to delete a data path from a storage policy copy:

  1. From the CommCell Browser, expand Policies | Storage Policies | storage policy.
  2. Right-click the appropriate storage policy copy and click Properties.
  3. On the Copy Properties dialog box, click the Data Paths tab.
  4. Select the appropriate data path to be deleted, and then click Delete.
  5. Click OK.