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PowerScale OneFS 9.5.0.0 CLI Administration Guide

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Fail back data to a primary cluster

After you fail over to a secondary cluster, you can fail back to the primary cluster.

CAUTION:Before you begin, we recommend that you run SyncIQ's resync-prep job as soon as possible before the fail back. The resync-prep job sets the dataset on the primary cluster to read-only, which will prevent any possible writes from occurring. Only run the resync-prep job if the allow-writes are not going to be reverted. Note that if writes have occurred on the primary cluster, then resync-prep will revert those changes. Creating a temporary snapshot is a safeguard to reduce risk of data loss if a failover-failback is performed incorrectly. You must take a snapshot on the SyncIQ source path prior to resync-prep if that data needs to be preserved. This is to prevent situations in which both clusters are in a writable state during fail over, when clients could potentially be writing to both clusters.

Before you can fail back to the primary cluster, you must already have failed over to the secondary cluster. Also, you must ensure that your primary cluster is back online.

  1. Create mirror policies on the secondary cluster by running the isi sync recovery resync-prep command on the primary cluster.
    The following command creates a mirror policy for weeklySync: 
    isi sync recovery resync-prep weeklySync
    SyncIQ names mirror policies according to the following pattern: 
    <replication-policy-name>_mirror
  2. Before beginning the failback process, prevent clients from accessing the secondary cluster.
    This action ensures that SyncIQ fails back the latest data set, including all changes that users made to data on the secondary cluster while the primary cluster was out of service. We recommend that you wait until clients are inactive before preventing access to the secondary cluster.
  3. On the secondary cluster, run the isi sync jobs start command to run the mirror policy and replicate data to the primary cluster.
    The following command runs a mirror policy named weeklySync_mirror immediately: 
    isi sync jobs start weeklySync_mirror
    Alternatively, you can modify the mirror policy to run on a particular schedule. The following command schedules a mirror policy named weeklySync_mirror to run daily at 12:01 AM: 
    isi sync policies modify weeklySync_mirror --enabled yes 
--schedule "every day at 12:01 AM"
    If specifying a schedule for the mirror policy, you need only allow the mirror policy to run once at the scheduled time. After that, you should set the mirror policy back to a manual schedule.
  4. On the primary cluster, allow writes to the target directories of the mirror policy by running the isi sync recovery allow-write command.
    The following command allows writes to the directories specified in the weeklySync_mirror policy: 
    isi sync recovery allow-write weeklySync_mirror
  5. On the secondary cluster, complete the failback process by running the isi sync recovery resync-prep command for the mirror policy.
    The following command completes the failback process for weeklySync_mirror by placing the secondary cluster back into read-only mode and ensuring that the data sets are consistent on both the primary and secondary clusters. : 
    isi sync recovery resync-prep weeklySync_mirror

Direct clients back to the primary cluster for normal operations. Although not required, it is safe to remove a mirror policy after failback has completed successfully.

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