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14 PS Series Asynchronous Replication Best Practices and Sizing Guide | BP1012
With replication, it does not matter if the volume is thin provisioned or uses a traditional volume. In either
case, only the data that has changed will be copied to the replica. On the secondary side, volumes are always
thin provisioned to conserve available capacity used by the replica reserve for that volume.
3.4 Fast failback
With fast failback enabled, you can ensure that the volume data preserved by the failback snapshot on the
primary group always matches the volume data in the most recent replica stored on the secondary group. If
you have an event that causes failover to the secondary group and the workload subsequently writes changes
to the replica volume, failback snapshot supports a quicker failback to the primary group by replicating only
the changes made to the replica volume during the time it was active as a recovery volume on the secondary
group. If the failback snapshot is not enabled, you must replicate the entire volume contents back to the
primary group to complete the failback operation. Depending on the size of the volume, the failback scenario
can take significantly longer to complete if fast failback is not enabled.
3.5 Space borrowing for replication
PS Series firmware version 8.0 provides the ability for snapshots, local and remote replicas, and deleted
volumes in the Group Volume Recovery Bin to temporarily borrow space beyond the configured reserves.
This feature, called space borrowing, simplifies configuring reserve space, improves space utilization, and
enhances management of snapshots and replica reserves.
While it is possible to enable or disable space borrowing for snapshots, space borrowing for replication is
automatic and cannot be disabled.
Remote replicas can borrow beyond their total replica reserve, but the total amount of configured reserve
space must still fit within the delegated space. If there is insufficient delegated space on the secondary group,
the system requires manual administrative intervention to increase the amount of delegated space.
Also, if the replica reserve for a volume is configured with a very low value, such as the minimum 105%, the
system can potentially require manual administrative intervention to increase the reserve percentage so that
an in-progress replica can continue. In-progress replicas are not eligible to borrow space.
Note: To use space borrowing for replicas, all members in the secondary group must be running PS Series
firmware version 8.0 or later. Space borrowing for snapshots requires PS Series firmware v6.0 or later. For
more information on space borrowing, refer to Space Borrowing for Snapshots and Replicas.