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Replication and remote recovery
62 Dell EMC SC Series: Best Practices with VMware vSphere | 2060-M-BP-V
data centers. Because of the nature of the proxied I/O, any disruption to the link or primary Live Volume
causes the secondary Live Volume datastore to become unavailable as well. If for any reason the primary
Live Volume goes down permanently, the administrators need to perform a recovery on the secondary Live
Volume from the last known good snapshot. The DSM replication disaster recovery wizard is designed to help
with this type of recovery.
15.4.2 Synchronous Live Volume
SCOS 6.5 introduced synchronous capabilities to Live Volume using the newly revamped sync replication
engine added in a previous release. Synchronous (sync) Live Volume is a new disaster recovery option to
save time and effort recovering virtual machines. Since the disk signatures of the datastores remain the same
between sites, volumes do not need to be resignatured, nor do virtual machines need to be re-added to
inventory. When using sync Live Volume without automatic failover enabled, the disaster must still be
declared through DSM to bring the secondary Live Volumes online. Saving most of the laborious recovery
steps previously required, and virtual machines can be powered on after the volume comes online and the
host has been rescanned.
One key consideration to using sync Live Volume is that round-trip link latency is an important factor for
application performance. In relation, the high consistency mode is the default option to ensure data integrity,
meaning that low latencies are especially important. Sync Live Volume is most practically used within a data
center or a campus environment where round-trip link latency can be kept low. Although round-trip latencies
between sites have no hard-set limitation, it is limited by the tolerances for each application or VMware
support tolerances as noted previously.
For more information about Live Volume, consult the paper, Dell EMC SC Series Storage: Synchronous
Replication and Live Volume.
15.4.3 Live Volume automatic failover
When using SCOS 6.7 or later, Live Volume automatic failover may be used for stretched cluster
configurations such as the vSphere Metro Storage Cluster (vMSC) solution certified by VMware. When using
DSM as a tiebreaker at an independent third site, it allows multiple SC Series arrays to survive an entire array
failure for increased storage availability scenarios.
For more information about the Live Volume vMSC solution, consult the VMware Knowledge Base article,
“Implementing vSphere Metro Storage Cluster using Dell Storage Live Volume (2144158)”, and the Dell paper
Dell EMC SC Series Storage: Synchronous Replication and Live Volume.
15.5 Replication tips and tricks
Since replicated volumes often contain more than one virtual machine, it is recommended that virtual
machines are sorted into specific replicated and non-replicated volumes. For example, if there are 100 virtual
machines in the ESXi cluster, and only eight of them need to be replicated to the DR site. A special replicated
volume should be created to place the eight virtual machines.
As mentioned previously, if separation proves to reduce snapshot sizes, operating system page files should
be kept on a separate volume that is not replicated. That keeps replication and snapshot sizes smaller
because the data in the page file changes frequently and it is usually not needed for a system restore.
To set replication priorities, an administrator can take advantage of the SC Series QoS to prioritize replication
bandwidth of certain volumes. For example, if there is a 100 Mb connection between sites, two QoS