Image mode virtual disks (VDisks) enable you to import and then migrate existing data that is managed by the SAN Volume Controller cluster.
Ensure that you follow the guidelines for using image mode VDisks. This might be difficult because a configuration of logical disks and arrays that performs well in a direct SAN-attached environment can contain hot spots or hot component disks when they are connected through the cluster.
If the existing storage systems do not follow the configuration guidelines, consider stopping I/O operations on the host systems while you migrate the data into the cluster. If I/O operations are continued and the storage system does not follow the guidelines, I/O operations can fail at the hosts and ultimately loss of access to the data can occur.
The procedure for importing managed disks (MDisks) that contain existing data depends on the amount of free capacity you have in the cluster. You must have the same amount of free space in the cluster as the data that you want to migrate into the cluster. If you do not have this amount of available capacity, the migration causes the MDisk group to have an uneven distribution of data because some MDisks are more heavily loaded than others. Further migration operations are required to ensure an even distribution of data and subsequent I/O loading.