About Failover And Failback; About Replication And Encrypted Recovery Points; About Retention Policies For Replication; Performance Considerations For Replicated Data Transfer - Dell DL4000 User Manual

Because large amounts of data need to be copied to the portable storage device, an eSATA, USB 3.0, or
other high-speed connection to the portable storage device is recommended.

About failover and failback

In the case of a severe outage in which your source core and protected machines fail, your DL Appliance
supports failover and failback in replicated environments. Failover refers to switching to a redundant or
standby target Core upon system failure or abnormal termination of a source core and associated
protected machines. The main goal of failover is to launch a new agent identical to the failed agent that
was protected by the failed source core. The secondary goal is to switch the target core into a new mode
so that the target core protects the failover agent in the same way as the source core protected the initial
agent before the failure. The target core can recover instances from replicated agents and immediately
commence protection on the failed-over machines.
Failback is the process of restoring a protected machine and core back to their original states (before
failure). The primary goal of failback is to restore the protected machine (in most cases, this is a new
machine replacing a failed agent) to a state identical to the latest state of the new, temporary agent.
When restored, it is protected by a restored source core. Replication is also restored, and the target core
acts as a replication target again.

About replication and encrypted recovery points

While the seed drive does not contain backups of the source core registry and certificates, the seed drive
does contain encryption keys from the source core if the recovery points being replicated from source to
target are encrypted. The replicated recovery points remain encrypted after they are transmitted to the
target core. The owners or administrators of the target core need the passphrase to recover the
encrypted data.

About retention policies for replication

The retention policy on the source core determines the retention policy for the data replicated to the
target core, because the replication task transmits the merged recovery points that result from a rollup or
ad-hoc deletion.
NOTE: The target core is not capable of rollup or of ad-hoc deletion of recovery points. These
actions can only be performed by the source core.

Performance considerations for replicated data transfer

If the bandwidth between the source core and the target core cannot accommodate the transfer of
stored recovery points, replication begins with seeding the target core with base images and recovery
points from the selected servers protected on the source core. The seeding process only has to be
performed once, as it serves as the foundation that is required for regularly scheduled replication.
When preparing for replication, you must consider the following factors:
Change Rate The change rate is the rate at which the amount of protected data is accumulated.
The rate depends on the amount of data that changes on protected volumes and
the protection interval of the volumes. If a set of blocks change on the volume,
reducing the protection interval reduces the change rate.
Bandwidth The bandwidth is the available transfer speed between the source core and the
target core. It is crucial that the bandwidth be greater than the change rate for
replication to keep up with the recovery points created by the snapshots. Due to
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