Administrator Guide

Live Volume overview
43 Dell EMC SC Series: Synchronous Replication and Live Volume | CML1064
present on the connection, Dell Storage recommends disabling Deduplication for Live Volumes in order to
preserve controller CPU time for other processes.
Replicate Active Snapshot: It is recommended that Replicate Active Snapshot is enabled for asynchronous
Live Volumes. This ensures that data is replicated in real time as quickly as possible which decreases the
amount of time required to perform a Live Volume Swap role. For Live Volumes configured with either mode
of synchronous replication, the Active Snapshot is effectively replicated in real time providing the replication is
in sync (HA mode) and not paused by an administrator (HA and HC modes).
Replicate Storage to Lower Tier: The Replicate Storage to Lowest Tier feature is automatically enabled for
a new Live Volume. Disable this option to replicate data to tier 1 on the destination array. Many users perform
the initial Live Volume replication to the lowest tier, and then deselect this option once the initial replication
completes. This strategy aids in preserving tier 1 storage capacity, which is useful when using SSD or 15K
drives. For more information on Data Progression with Live Volume, see the section, Data Progression and
Live Volume.
QoS Nodes: A pair of QoS Nodes depicts the desired egress traffic shaping to be applied when replicating
from the primary to the secondary Live Volume. Although labeled a secondary QoS Node, it does not provide
ingress traffic shaping. Instead, it provides egress traffic shaping after a role swap occurs and it becomes the
primary Live Volume. QoS Nodes apply to replication traffic only. The Live Volume proxy traffic between the
arrays is not governed by QoS Nodes. If the link between the Live Volume storage controllers is shared by
other traffic, it may be necessary to throttle the replication traffic using QoS Nodes to prevent it from flooding
the replication link. However, throttling synchronous replication traffic will produce latency for applications
which are dependent on the Live Volume. For this reason, replication links and QoS Nodes should be sized
appropriately taking into account the amount of data per Live Volume, rate of change, application latency
requirements, and any other applications or services that may be sharing the replication link. This is
especially important when using synchronous replication. Note that vSphere Metro Storage Cluster latency
between sites should not exceed 10 ms.
For instance, if a 20 Gbps replication link exists between data centers that is shared by all intra-data-center
traffic, a replication QoS could be set at 10 Gbps and thereby limits the amount of bandwidth used by
replication traffic to half of the pipe capacity. This allows the other non-Live-Volume replication traffic to
receive a reasonable share of the replication pipe, but could cause application latency if synchronous
replication traffic exceeds 1,000 MBps.