V11 SP8

CommCell Scalability Guide

Table of Contents


Certain guidelines associated with the design, deployment, and support of large CommCell® environments must be followed.

Benefits of Multiple CommCells

The following list outlines the benefits gained by deploying Commvault® software across multiple CommCell groups in an extra large environment:

  • General IT Maintenance

    Allows for partial downtime of backup operations. For example, when a CommServe group is taken offline for software updates/upgrades or hardware upgrades and maintenance, the other CommCell groups will continue to function without impact on data movement operations.

  • Reduce Risk Associated with Unreliable IP Networks

    The strategic placement of CommServe within the shortest network distance to the servers it protect, dramatically reduces issues associated with slow or unreliable network connectivity between LAN clients and the CommServe.

  • Improved CommCell® Group Activity Monitoring and Performance

    By balancing data protection activity load across multiple CommServes, a smoother operation of the CommCell group is allowed, with better response time in each individual CommCell console GUI.

  • Load Balancing on Resources

    As the data protection infrastructure evolves, Commvault® provides an easy-to-use method for maintaining the balance of resources across CommCell groups via CommCell Migration.

Planning CommCell Deployment

This section suggests the deployment requirements and considerations to be taken into account for a medium, large, or extra large environment. Each size environment has different hardware and software requirements.

Deployment Requirements

Consider the requirements described in CommCell Sizing as you plan how you will install and configure Commvault®:

Assessing Future Growth

It is important to complete an accurate assessment of data growth planned, during completion of CommCell® design configuration.

This ensures that the design aligns with the scalability requirements reflected in this document when calculating backups, media utilization and retention requirements.

Scalability Factors

Commvault can handle up to 20,000 servers or 50,000 laptops in a single CommCell environment. By default, the software supports 4,000 servers or laptops out of the box. The actual number of servers and laptops might vary based on:

  • Hardware Specifications of your CommCell environment
  • Operational parameters in the CommServe, such as:
    • Number of jobs running in a 24-hour period
    • Number of jobs completed in a single attempt
    • Type of jobs
    • Geographical client locations (LAN versus WAN)

We recommend that you regularly check the health and activities of your CommCell environment to prevent it from reaching the built-in scalability limits. You can do this by enabling data collection on the CommCell and requesting diagnostic reports as described in Configuring Cloud Metrics Reporting.

When the CommServe database approaches the built-in scalability limits (at 90% a warning is issued to the Administrators), you must contact your Account team to evaluate the health of your environment. They will advise you whether you need to create a new CommCell or if the scalability limits can be increased.

Adding More Clients to your CommCell Environment

By default, Commvault supports 4,000 servers or laptops out of the box. If you need more than 4,000 clients, contact your software provider to request an increase.

When a request is made, the software provider will ask you to provide diagnostic reports to analyze your environment. Field Engineers will also be sent to test your CommCell environment on-site and determine if the scalability limits can be increased.

After the request is approved, an increase of 1,000 clients will be configured for your environment. The number of clients is increased by 1,000 per request to ensure that the CommCell performance is not compromised.

Improving the Scalability of a CommCell

It is strongly recommended that the soft limits mentioned in the sections below are followed, and not be exceeded.

It is also recommended that you review the Deduplication Architecture Guide when planning for Commvault® Block Level Deduplication CommCell group deployments. Contact Customer Support or your Account Team for the current release of that separate document.

Increasing Streams for Concurrent Backups

To increase the number of streams for concurrent backups from a large number of clients, enable the option optimize for concurrent backups. It will increase the current stream count limit by 200 more streams.

  1. From the CommCell Browser, navigate to Storage Resources | MediaAgents | <MediaAgent>.
  2. Right-click the MediaAgent that you wish to optimize for concurrent LAN backups and then click Properties.
  3. From the MediaAgent Properties dialog box, click the Control tab.
  4. In the Data Transfer section, select the Optimize for concurrent LAN backups check box to enable the option.
  5. Click OK.

Disconnecting Idle GUI Connections

To improve the performance of the CommServe, use the option that disconnects idle GUI connections. When idle GUI connections are disconnected, other GUIs can connect without exceeding the established parameter.

  1. From the CommCell Console ribbon, on the Home tab, click Control Panel.
  2. Under CommCell, click the System icon.
  3. On the General tab, select the Allow GUI connections to timeout check box.
  4. Enter a timeout value in the GUI Timeout in minutes box.

    The recommended value is 30 minutes, however the default value is set to 180 minutes.

    Tip: Enter a reasonable timeout value to programmatically terminate idle connections. The lower the disconnect threshold value, the sooner the idle GUIs will be disconnected, allowing active GUI sessions to connect to the CommServe.

  5. Click OK.

Decreasing Network Agents for Non-LAN Optimized Backups

For better throughput, specify a lower value for the number of data pipes/processes that the client uses to transfer data over a network.

  1. In the CommCell Browser, go to Client Computers > client > agent > backup set or instance.
  2. Right-click the subclient, and then click Properties.

    The Subclient Properties dialog box is displayed.

  3. For file system subclients, do the following:
    1. Click Advanced.

      The Advanced Subclient Properties dialog box is displayed.

    2. On the Performance tab, in the Resource Tuning section, enter 1 in the Network Agents box.

      Note: On non-UNIX computers, the default value is 2 and a maximum of 4 can be established if necessary. On UNIX computers the default value is 1 and a maximum of 2 can be established if necessary.

  4. For non-file system subclients, do the following:
    1. On the Storage Device tab, click the Data Transfer Option tab.
    2. In the Resource Tuning section, enter 1 in the Network Agents box.
  5. Click OK.

Managing Concurrent Jobs

It is important to manage concurrently running jobs by staggering schedules. Use multiple schedule policies on different client groups and adjust the timing of the schedules in order to optimize scalability. The table below displays the maximum number of concurrent job streams permitted in different environments. For information on configuring the permitted number of job streams, see Setting the Maximum Number of Simultaneously Running Streams.

CommCell Class Total Permitted Job Streams
Medium 1 to 100
Large 101 to 300
Extra Large 301 to 1,000


  • There is no limit to the number of Storage Policies in a single CommCell Group for the extra large environments.
  • Stagger the start time of jobs by a time interval of up to 20 minutes.

Tuning the SQL Server Memory Usage

If you pre-installed the SQL Server and then installed the CommServe software, we recommend that you verify the SQL memory usage. The maximum memory used by the SQL Server should be 50% of the physical memory available in the CommServe computer.

Use the following steps after the CommServe software is installed:

  1. On the CommServe computer, open the Microsoft SQL Server Management Studio.
  2. Right-click the Server_Instance, and then click Properties.
  3. From the Server Properties dialog box, on the left pane, select the Memory page.
  4. In the Maximum server memory (in MB) box, specify 50% of the physical memory available in the computer.
  5. Click OK.

Reducing Subclient Count

Subclient count optimization allows managing the daily backup operations easily for the administrator. It is recommended to periodically review the subclients in order to determine if any redundant or unneeded subclients exist and can be removed from the CommCell configuration. Information about each subclient is tracked by the CommServe, and by reducing the number of subclients, there is a huge reduction in the amount of tracking information.

Increasing Chunk Size for Tape Backups

This parameter affects tape backup operations. A higher chunk size gives a better throughput. A lower value for this setting is recommended for frequent checks against slower data protection operations, especially when data is moving across a WAN link.

  1. On the ribbon in CommCell Console, click the Storage tab, and then click the Media Management.
  2. From the Media Management Configuration dialog box, click the Chunk Size tab.
  3. Click the <Agent>, and enter 8 in the Chunk Size (MB) column.

    • Granular restores will be slower using this setting, however, large restores will be faster.
    • This setting does not apply to database backups where the chunk size is 16GB by default.

  4. Click OK.

Increasing the Completion Rate of High Frequency Transaction Log Backup Jobs

This setting is recommended for large CommCells that have multiple remote sites where each remote site has its own dedicated resources because keeping resource reservations cached will increase the overall job completion rate.

However, since the cached resources are not available to other subclient jobs, this option is not recommended for storage policies used for a large number of subclients where the frequency of the backups is staggered.

  1. Locate the storage policies where you want to cache the reserved resources for backup jobs.
  2. From the CommCell Browser, navigate to Policies | Storage Policies.
  3. Right-click the <Storage Policy> and then click Properties.
  4. From the Storage Policy Properties dialog box, click the General tab.
  5. Select the Keep resource reservations cached for jobs on this storage policy check box.
  6. Click OK.

Managing Hardware Snapshots

There is no software limit on the number of hardware-generated Snapshots using Commvault®. However for limits imposed by each manufacturer’s controllers and software, refer to your hardware provider's documentation.

Setting Up Fan-In Ratio for Connections to a CDR Destination

For optimal performance, the total number of Replication Pairs configured for the same source volume should be kept to a minimum. If multiple Replication Pairs for the same source volume are required, the following limits must be observed.

CommCell Class FAN IN Ratio for Different Server Types
Win 32 Win 64
Medium 1 to 20 1 to 60
Large 21 to 50 61 to 150
Extra Large 51 to 100 151 to 500


  • Ensure Test Unit Ready registry key is set properly on all Microsoft Windows servers that have visibility to SAN-attached tape drives.

    Additional detail regarding this registry key is available at: http://support.microsoft.com/default.aspx?scid=kb;en-us;842411&Product=w

  • In a Dynamic Drive Sharing (DDS) environment, configure between a minimum of 2 to a maximum of 6 drives that are controlled through each MediaAgent.

    This will allow for jobs to meet the backup window needs at the same time and not overload a single MediaAgent within the network.

    Associate Storage Policies and MediaAgents evenly with backups in order to balance the data protection operations.

  • To enhance the scalability of the auxiliary copy operation and for load-balancing between the CommServe and the MediaAgent resources, ensure that Use Scalable Resource Allocation check box is selected when running an auxiliary copy operation.

    For more information, see Performing an Auxiliary Copy.

File System iDataAgent

File System Multi-Streaming employs multiple data streams per subclient for the data protection operation, enabling the subclient's contents to be distributed to all the streams, transmitting them in parallel to the storage media. We recommend you to use File System Multi-Streaming for larger subclients (1TB or more).

It allows the file system backup to use multiple readers for increased performance, this configuration in turn reduces duplicate file Scan Time on client servers.

For subclients less than 1TB in total size, set the number of readers on the sub-client to 1.

Reducing the Number of Backup Jobs in Waiting

In a large environment, when there are many backup jobs running, some of the backup jobs move into Waiting state as a result of resources being in contention for running Auxiliary copy jobs. You can use the available resources efficiently and reduce the number of backup jobs in Waiting state by setting the following configurations.

  • Specify the number of backup jobs that move into Waiting state when Auxiliary Copy jobs are running. When the number of Waiting backup jobs exceeds this threshold, the resource allocation request for the Auxiliary Copy jobs that are running is skipped until the number of backup jobs fall below the threshold limit.

    You can set this limit based on the number of backup jobs running and the number of available resources.

    1. On the ribbon in CommCell Console, click the Storage tab, and then click Media Management.
    2. From the Media Management Configuration dialog box, click the Auxiliary Copy Configuration tab.
    3. In the Skip AuxCopy Reservation request when backup jobs in waiting state exceeds box, enter the limit for backup jobs, and then click OK.
  • Increase the time interval before all disk volumes are marked as full.
    1. On the ribbon in CommCell Console, click the Storage tab, and then click Media Management.
    2. From the Media Management Configuration dialog box, click the Service Configuration tab.
    3. In the Interval (hours) between marking large disk volumes full box, enter the time interval for backup jobs, and then click OK.
  • For better tape utilization:

    Ensure that you re-use appendable media for new jobs. Increase the number of days that you can use the media after it is marked as appendable.

    1. From the CommCell Browser, expand Storage Resources | Libraries.
    2. Right-click the appropriate tape library, and then click Properties.
    3. In the Library Properties dialog box, click the Media tab, specify the following settings, and then click OK.
      1. Select the Mark Media Appendable and Use Appendable media check boxes.
      2. In the Use Appendable Media within n Day (s) of its last write time box, type the number of days.
    When a job requires a media, ensure that recycled media is used before any other media.
    1. From the CommCell Browser, expand Storage Resources | Libraries | <Tape Library> | Media By Group.
    2. Right-click the appropriate scratch pool and then click Properties.
    3. In the Spare Group Properties dialog box, ensure that the Use most reused media first check box is selected, and then click OK.