Dell EMC Metro node 7.1 Administrator Guide

Synchronous consistency groups

Synchronous consistency groups provide a convenient way to apply rule sets and other properties to a group of volumes in a metro node Local or metro node Metro.

Metro node supports up to 1024 synchronous consistency groups.

A synchronous consistency group:

• Contains up to 1000 virtual volumes.
• Contains either local or distributed volumes, (but not a mixture of both).
• Contains volumes with either global or local visibility.
• Uses write-through caching (known as synchronous cache mode in the metro node user interface).

  Write order fidelity is maintained by completing all writes to disk before acknowledging the write to the host.

The following figure shows a synchronous consistency group that spans two clusters in a metro node Metro configuration.

• The hosts at both clusters write to the metro node distributed volumes in the consistency group.
• Metro node writes data to the back-end storage on both clusters
• An acknowledgment is returned to the host that is issuing the write.

This guarantees that the image on the back end storage is an exact copy on both sides.