Thanks for the information, very useful. I now realize that unless we have a large snapshot size that is definitely bigger than any changes to the main volume corruption can occur as snapshot space is exhausted.

So make sure snapshot volumes are big enough!

In fact what we're doing now is when we want to copy a large amount of data over we just turn off the snapshot task make sure current running task is all finished then do the copying, turn task back on when copying completed.

It then seems that the data replication can catch up with all the changes made since the task was stopped?

Have I got this right?