Administrator Guide

Synchronous replication use cases
23 Dell EMC SC Series: Synchronous Replication and Live Volume | CML1064
asynchronous replication. Adding significant distance between sites generally results in latency increases
which will still be observed in the applications at the source side for as long as the high availability replication
is in sync.
Finally, if virtual machines are deployed in a configuration that spans multiple volumes, consider using Replay
Manager or consistency groups. Replay Manager is covered in section 11.6.
High availability synchronous with consolidated vSphere or Hyper-V sites
A replication link or destination volume issue in St. Paul results in no VM outage in Minneapolis
Note: Consistent snapshots may be created for asynchronous and synchronous replications. However,
Consistent snapshots are not supported with Live Volumes.
4.3.2 Microsoft SQL Server and Oracle Database/Oracle RAC
As discussed in section 4.3.1, the behavioral delta between high availability and high consistency modes is
minimal until extreme latency or an outage impacts the destination volume availability. If high availability
synchronous replication falls into an out-of-date state, write I/O at the source volume is journaled and the
destination volume becomes inconsistent. In terms of recovery, this may or may not be acceptable. A feature
in Dell Storage Manager advises customers on whether or not the active snapshot on the destination volume
is safe to recover from at a data consistency level. In the event that DSM detects the data is not consistent,
the recommendation is to revert to the most recent consistent snapshot associated with the destination
volume (another new feature in synchronous replication: replication of snapshots).
For storage hosts with data confined to a single volume, special considerations are not necessary. However,
if the host has application data spread across multiple volumes (for example, a VM with multiple virtual
machine disk files, or a database server with instance or performance isolation of data, logs, and other files)
then it becomes critical to ensure snapshot consistency for the replicated data that will be used as a restore
point. Ensuring all volumes of a dataset are quiesced and then snapped at precisely 8:00, for example,
provides a data consistent restore point across volumes supporting the dataset. This snapshot consistency is