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What are SMB Continuously Available (CA) Shares

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Applies to

  • ONTAP 9
  • Continuously Available (CA)


  • Continuously Available (CA) is a share property that, by using SMB3 scale-out, persistent handles, Witness, and transparent failover, allows file shares to be accessible during otherwise disruptive scenarios such as controller upgrades or failures.


ONTAP supports CA shares for both Hyper-V over SMB and SQL Server over SMB use cases

  • CA Shares are supported in ONTAP 8.2 and later, supported for SMB shares for both Hyper-V virtual machine files or SQL Server system databases and user databases on volumes residing in Storage Virtual Machines (SVMs) with FlexVol volumes and FlexGroups (9.6+), while at the same time providing nondisruptive operations (NDOs) for both planned and unplanned events.
  • Nondisruptive operations for Hyper-V and SQL Server over SMB refers to the combination of capabilities that enable the application servers and the contained virtual machines or databases to remain online and to provide continuous availability during many administrative tasks
  • This includes both planned and unplanned downtime of the storage infrastructure.
  • Supported nondisruptive operations for application servers over SMB include the following:
    • Planned takeover and giveback
    • Unplanned takeover
    • ONTAP upgrade
    • Planned aggregate relocation (ARL)
    • LIF migration and failover
    • Planned volume move
  • Along with the release of SMB 3.0, Microsoft has released new protocols to provide the capabilities necessary to support nondisruptive operations for Hyper-V and SQL Server over SMB.
  • Data ONTAP uses these protocols when providing nondisruptive operations for application servers over SMB:
    • SMB 3.0
    • Witness
      • The Witness protocol provides enhanced client failover capabilities for SMB 3.0 continuously available shares
      • Witness facilitates faster failover because it bypasses the LIF failover recovery period
      • It notifies Hyper-V servers when a node is unavailable without needing to wait for the SMB 3.0 connection to time out
      • SMB Witness requires TCP 40001 to be unblocked.
Active IQ System Risk Detection
  • For customers who have enabled AutoSupport™ on their storage systems, the Active IQ Portal provides detailed System Risk reports at the customer and site and system levels
  • The reports show systems that have specific risks as well as severity levels and mitigation action plans
  • You may be reading this article as a result of one of those alerts
  • If CA Share is detected on cifs shares on your system, please ensure that it’s under the currently supported use cases
  • Because ONTAP cannot discern what client connections are from Hyper-V or SQL over SMB versus normal file operations, we have implemented At-Risk Signature (ARS) to warn customers of CA share usage
  • If you have performed diligence in ensuring proper use cases are deployed in your environment for CA shares, you may ignore these warnings.

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