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ShadowSnap's Interaction with iSCSI volumes



This article discusses the interaction between the ShadowSnap agent, Datto Windows Agent, and Agentless systems with any locally connected iSCSI volumes.


Below are resources about the Microsoft iSCSI Software and how it works:

iSCSI Volumes and ShadowSnap or Datto Windows Agent systems

iSCSI volumes are useful solutions for expanding storage and allowing multiple machines to interact with a single storage volume. Due to their typically dynamically expanding nature, iSCSI volumes in dynamic configurations will contract and expand as required. This causes issues when Datto agents take a backup of the protected volume. If the volume has expanded, ShadowSnap or DWA must create a new sparse image.

iSCSI is also used by the Datto solution to perform file restores where the original security permissions must be retained by the restore.

Even a consistently shrinking volume may run into issues when protected by the Datto appliance. Since the local agent's backup operation is to determine the disk configuration from Windows, it will attempt to back up drives that appear as local volumes. Differential merges will occur on the volumes as they change their configurations.

Also, if the session state gets disconnected when backing up an iSCSI volume, it can cause the volume state to activate a new session ID. This will cause a differential merge, as the incremental tracking state is reset. It potentially can cause an error as such:

        -initiator: Session state timeout occurred, or a session
            reinstatement cleared this session instance.  This results
            in the freeing of all associated resources and the session
            state is discarded.
        -target: Session state timeout occurred, or a session
            reinstatement cleared this session instance.  This results
            in the freeing of all associated resources and the session
            state is discarded.

Agentless Systems and iSCSI

The agentless backup system uses the VMWare snapshot feature on the host to capture local changes.  Therefore, it does not support backing up iSCSI storage that is connected directly to the Guest OS itself; these drives will not be detected.

An iSCSI disk attached through the VM template in VMWare can be detected and backed up. However, depending on how it is set up on the storage side, it can encounter the same issues as agent based backups, discussed above.

Microsoft iSCSI Updates

  • Microsoft has two locations for iSCSI specific software packages. Ensure that the latest versions are always being used upon setup and configuration.
  • When setting up volumes for backup, make sure the volumes appear as locally accessible volumes on the target server and, once configured, will not be manipulated.
  • Configurations of these volumes are beyond the scope of Datto Technical Support.

Additional Resources

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