It is confusing me and need someone to confirm. when we take snapshots through snapcenter plugins such as for VMWare, SQL or Unix file systems, the snapshot actually being taken on VM, SQL database or Unix file system only or on whole NetApp volume? let us assume the volume has more other items. Since the snapshot happens on source group which includes VMs, databases or file systems. I assume the snapshots happen on individual items instead of whole volume and only data in snapshots will be snapmirrored. Can someone please correct me if I am wrong. thanks for sharing.
The term Snapshot is ambiguous. There are VMware VM Snapshots that are independent of NetApp storage system snapshots. When a NetApp storage system Snapshot is taken it is a volume Snapshot. All the blocks that are in use on the volume are locked and any new writes are to new blocks. A volume Snapshot is of the whole volume. When changes are made, the inode map is updated for the live file system to point to the new data. That's the reason Snapshots grow over time. We have to have accounting of where the space is going so the block that is only used by the Snapshot is assigned as space used by the Snapshot.
Frequently a VM Snapshot is taken and then a storage system Snapshot is taken. Backup of VMs is complicated because there are several layers to consider. We need to have things in a consistent state for the backup of applications and operating systems. So we have plug-ins on the operating system that quiesce the applications like SQL to put them into a consistent state. Then VMware tools will put the VM operating system into a consistent state for the VMware snapshot of the virtual machine. And finally a volume Snapshot is taken of the storage system volume that contains the VM in a consistent state and the application quiesced.
A mirrored volume will have all the blocks of the source volume. We have a base Snapshot so we only have to transfer the changes but the destination will have block copies of all the data on the source volume.
To directly answer your question a volume Snapshot is of the whole volume. It will contain all the VMs on the volume even though they may not be in a consistent state.
The concepts touched on by your question are well beyond a few paragraphs of explanation. Below are some links you may find helpful. Please ask if you need clarification of any of these points.