If the grids are in the same Data Center and on the same local network (i.e. connected to the same switch), then the copy speed it usually about 1GB of volume size per minute. So if your disk size (volume) is 40GB, then it will take about 40 minutes to copy it.

The formula is:

Time to stop the application + time to copy volume (1GB per minutes) + time to start the application = migration downtime.

If the grids are in different Data Centers, then the migration is much slower. DNS Europe Data Centers are connected by very high speed links, but any copy that takes place on the internet is subject to transient conditions that affect speeds. The copy may take up to 10 or 20 times longer.