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Frequently Asked Questions (FAQs) for Auxiliary Copy

Table of Contents

How does Dynamic Streaming Allocation work?

During Auxiliary Copy operation data is transferred from primary storage (source) to secondary storage (destination) which could be either tape or disk, with fixed number of source and the destination streams. During backup operation, if the backup data was not evenly distributed among the source streams, then Auxiliary Copy operation may not use all available streams in parallel as one stream may take longer to copy than another. In order to utilize all streams and improve copy performance, you can use Auxiliary Copy operation with Dynamic Stream Allocation.

Dynamic Stream Allocation reads the data from the primary storage and distributes the data evenly across all streams. This feature is more effective when you have Combine Source Data Streams and Multiplex source streams options enabled on a secondary copy and the destination copy is associated with a tape library. Use this feature when you have to copy large amount of data to a tape library.

For example, the following image and graph displays how the data is distributed across streams for storage policies with and without Dynamic Stream Allocation for below criteria:

  • Total data to copy is 1.4 TB
  • Data from client to primary storage was distributed using 8 data streams.
  • On the Storage Policy Copy properties, if you have Combine source data streams set to 2 streams and Multiplexing Factor set to 15.
  • Secondary Copy is using a library which has 2 drives.

Note: Even if you have the Distribute data evenly among multiple streams for offline read operations option enabled, the data distribution on streams might not be uniform as it is also depends on the size of the backup and whether the data on the source is multiplexed.

For example, a synthetic full backup with 20TB of application size will use only 1 stream.

Data Distribution without Dynamic Stream Allocation

Distribution of data across streams when Dynamic Stream Allocation is not enabled on the Storage Policy.

In this situation, 2 streams will be used for the Auxiliary Copy operation but the data is distributed unevenly and the Combine source data streams and Multiplexing Factor has no impact.

 

Data Distribution With Dynamic Stream Allocation

Distribution of data across streams when Dynamic Stream Allocation is enabled on the Storage Policy:

In this situation, 2 streams will be used for the Auxiliary Copy operation but the data is distributed evenly.

 

How do I estimate the number of streams available for an Auxiliary Copy operation?

Following rules are used while calculating the number of streams available for the auxiliary copy operation:

Rule Example
If the Combined Source Data Streams option is selected on the secondary copy, the number of streams on the secondary copy will be equal to the number of combined data streams. Copy A is the source copy and copy B is the secondary copy. The following option is selected for Copy B,

Combine Source Data Streams to 1 Stream

Only one stream is used for the auxiliary copy operation. All streams from copy A get copied one after the other to copy B.

If the Combined Source Data Streams option is not selected, the number of streams on the secondary copy will be equal to the number of combined streams on the source copy. Copy A is the source copy and copy B is the secondary copy. The following option is selected for copy A:

Combine Source Data Streams to 1 Stream

Only one stream is used for the auxiliary copy operation. All streams from copy A get copied one after the other to copy B.

If Combined Source Data Streams option is not selected for the source copy or the secondary copy, then the available number of streams will be the minimum of the following:
  • Maximum device streams defined for storage policy
  • Maximum number of drives available among all data paths of the copy
Device Streams defined for a storage policy is 10 and the secondary copy is using a library which has 4 drives. In this situation, 4 streams will used for the auxiliary copy operation.

If the data is software-compressed, will it be uncompressed during the Auxiliary Copy operation?

No. If you have enabled the Software Compression for a subclient, then backup data will not get uncompressed during the Auxiliary Copy operation.

Can I perform Auxiliary Copy, Data Verification and Content Indexing operations simultaneously?

Yes. You can perform Auxiliary Copy, Data Verification and Content Indexing Operations simultaneously. When these operations are initiated, each operation utilizes single Auxiliary Copy manager process.

If the data on a source copy is hardware compressed, will it be uncompressed during the Auxiliary copy operation?

No.  The hardware compression is transparent. The hardware compressed data is uncompressed by the tape device on read, and recompressed during tape write.

How can I skip jobs that are associated with the media during an Auxiliary Copy operation?

If the Media associated with a source copy is not readable, and you would like to skip the jobs associated with the Media during Auxiliary Copy operation, then perform following steps:

  1. From the right pane of the CommCell Browser, right-click the copy containing the media to which you want to disable jobs, click View and then click Media.
  2. From the Media List dialog box, right-click on the media for which you wish to disable jobs and select Prevent Copy.

    To select multiple media items, hold down the Ctrl key, and right click on the media.

  3. Click Yes on the Confirmation message.

How to Re-Copy all jobs associated with a media?

The Re-Copy option allows you to select the existing jobs in the specified media for re-copy. When the re-copy option is selected the existing jobs will be deleted (that is the jobs listed on the original media will be removed and the new storage policy copies on the new media will be the only secondary copy) and selected for re-copy. If the source copy is not available for a job, the existing copy will be retained as is. Re-copy can be done only on media associated with a secondary copy.

To re-copy all jobs associated with a media:

  1. From the CommCell Browser, select Policies | Storage Policies <Storage Policy Name>
  2. Right-click the storage policy copy, point to View, and then click Media.
  3. In the Media List dialog box, select and right-click on the media for which you want to recopy the jobs, and then click Re-Copy.
  4. Click Yes on the Confirmation message.

    Note that when Re-Copy option is selected the existing jobs will be deleted and selected for re-copy

In what sequence is the data copied during an Auxiliary Copy operation?

During an Auxiliary Copy operation, the data is copied in the following sequence:

  1. A media which contains oldest backup job is copied first.
  2. When all the data from this media is copied, the other media with oldest backup job is selected for the copy from a drive pool.
  3. When all the media from the drive pool are copied, the oldest media from the other drive pool is selected for the copy.
  4. When all the media from a library are copied, the oldest media from the other library is selected for the copy.
  5. When all media associated with a MediaAgent are copied, the oldest media from the other MediaAgent is selected for the copy.

If the Auxiliary Copy operation is using multiple streams, the same sequence will be repeated on all the streams.

Why is Auxiliary Copy job getting queued?

The Auxiliary Copy job works as follows:

  • selects the list of backup jobs that are available for copy
  • completes by copying all those selected backup jobs
  • does not select any new backup jobs that are available after the Auxiliary Copy job was started

When this Auxiliary Copy job is running to copy the selected backup jobs, if any new Auxiliary Copy job is initiated that was scheduled, then that new Auxiliary Copy job goes into Queued state and continues once the existing Auxiliary Copy job is complete.

To enable or disable new auxiliary copy job queuing:

  • On the CommServe computer, add the QueueConflictingAuxCopyJobs additional setting with value 1.

    For instructions on adding the additional setting from the CommCell Console, see Add or Modify an Additional Setting.

    Refer to the following table for applicable values:

    Property Value
    Name QueueConflictingAuxCopyJobs
    Category CommServDB.GxGlobalParam
    Type Integer
    Value Select one of the following values:
    • 1 - new auxiliary copy jobs are queued and run only when running auxiliary copy job completes
    • 0 - the auxiliary copy job would no longer be queued

Note: When queuing of auxiliary jobs is disabled (i.e. the parameter value is set to 0), any new backup jobs executed and completed while an auxiliary copy operation is running will be replicated at the end of its successful current iteration.

Why does the value of data transfer differ in the Process Manager and Auxiliary Copy Job Details?

The value of Data Transferred in the Process Manager dialog box might differ with the value of Data Transferred on Network in the Streams tab of Auxiliary Copy Job Details dialog box.

This happens because the value in the Process Manager gets updated quickly compared to the job in the CommCell Console.

Can I preempt an auxiliary copy operation with another auxiliary copy operation?

Yes, you can preempt an auxiliary copy operation with another auxiliary copy operation by configuring a global parameter.

Procedure

  1. On the CommServe computer, add the RMAuxCopyInterruptAuxCopy additional setting with value y.

    For instructions on adding the additional setting from the CommCell Console, see Add or Modify an Additional Setting.

    Refer to the following table for applicable values:

    Property Value
    Name RMAuxCopyInterruptAuxCopy
    Category CommServDB.GxGlobalParam
    Type String
    Value Select one of the following values:
    • y - will insert the parameter in the table to preempt an auxiliary copy operation with another auxiliary copy operation
    • n - will delete the parameter from the table
  2. Set job priorities as per your requirement. For more information see, Job Priorities and Priority Precedence - Getting Started.

Result

The auxiliary copy jobs will be preempted based on the your job priority selection.

How does the source MediaAgent selection happen for an auxiliary copy operation?

For an auxiliary copy operation, the source MediaAgent selection is selected based on the destination data path configuration. Based, on the following, the MediaAgent selection is given the highest priority.

  • If a LAN-Free MediaAgent (the data path MediaAgent is same on both the source and the destination storage policy copies) is available between the source and the destination data path, then the least used LAN-free MediaAgent is selected first.
  • If destination data path configuration is set as Round-Robin between Data Paths, the least used source MediaAgent is selected.
  • For load balancing between available MediaAgents for auxiliary copy readers, enable the Honor load balance for picking read MediaAgent parameter and also set the data path configuration as Round-Robin between Data Paths on the source storage policy copy.
  • If destination data path configuration is set as Use Preferred Data Path or Use Alternate Data Paths and there is no LAN-free MediaAgent between source and destination, then the default MediaAgent is selected if that MediaAgent can access the source media.
  • If there is no LAN-free MediaAgent between the source and the destination and no MediaAgent has been specified, then the MediaAgent associated with the drive that has the required media is selected.

For more information on MediaAgent selection, see Prefer copy data paths for picking read MediaAgent.

Can I perform auxiliary copy of the data that contains corrupted chunk?

Yes, it can be done with the help of an additional setting. Add the EnableAuxCopyCorruptedChunk additional setting on the source MediaAgent and set the value to 1 to enable the setting. The setting allows auxiliary copy of the data that contains corrupted chunk. Generally, auxiliary copy fails for the data with corrupted chunk.

The setting is applicable only for a deduplication enabled source copy for which parallel copy is not enabled. Also, this setting is applicable only for specific types of corruptions. You are advised to contact the Customer Support before enabling this setting..

Procedure