Administrator Guide

Live Volume overview
40 Dell EMC SC Series: Synchronous Replication and Live Volume | CML1064
After the Live Volume is upgraded for ALUA capability, the last step is to choose whether or not to Report
Non-optimized Paths. The default action is to report non-optimized paths. However, if the storage host
operating system does not support ALUA but there is a desire to upgrade the Live Volume for ALUA support,
this option allows leaving the ALUA feature disabled from the viewpoint of the storage host operating system.
Report Non-optimized Paths option
Live Volumes which were upgraded for ALUA capability or created in SCOS 7.3 and natively have ALUA
capability cannot be downgraded or have their ALUA capability removed. However, the ALUA feature can be
disabled at any time by editing the Live Volume and unchecking the Report Non-Optimized Paths option.
5.4 Live Volume connectivity requirements
Live Volume connectivity requirements vary depending on intended use. For example, there are different
requirements for using Live Volume to migrate a workload depending on whether or not the virtual machines
are powered on during the migration.
From the Live Volume perspective and outside of automatic failover with vSphere Metro Storage Cluster or
Microsoft Server/Hyper-V clusters, there are no firm restrictions on bandwidth or latency. However, to proxy
data access from one SC Series array to another requires the Live Volume arrays to be connected through a
high-bandwidth, low-latency replication link. Some operating systems and applications require disk latency
under 10 ms for optimal performance. However, performance impact may not be effectively realized until disk
latency reaches 25 ms or greater. Some applications are more latency sensitive. This means that if average
latency in the primary data center to the storage is 5 ms for the volume and the connection between the two
data centers averages 30 ms of latency, the storage latency writing data to the primary Live Volume from the
secondary Live Volume proxy across the link is probably going to be 35 ms or greater. While this may be
tolerable for some applications, it may not be tolerable for others.
If the Live Volume proxy communication or synchronous replication is utilized, it is strongly recommended to
leverage site-to-site replication connectivity which offers consistent bandwidth and the least amount of
latency. The amount of bandwidth required for the connectivity is highly dependent on the amount of changed
data that requires replication, as well as the amount of other traffic on the same wire. If a site is not planning
to proxy data access between arrays with asynchronous replication, then latency is not as much of a concern.