For each new warm migration with preloaded seed that you initiate, the seed is used to perform the initial synchronization between the source and target VM. After the initial synchronization finishes, vCloud Director Extender sends only deltas to the target VM.
Due to VM size or network bandwidth, the initial full sync might take a long time. Therefore, you might choose to copy the source VM to the target cloud site by using removable media, or other means of data transfer. Then you can run a warm migration with a preloaded seed and use the VM copy on the target cloud site as a preloaded seed. When a warm migration is set to use a seed, vCloud Director Extender does not copy the whole source VM to the target cloud site. Instead, it copies to the seed vApp only the different blocks between the source VM and the seed.
vCloud Director Extender stores the replication data in the seed vApp. No copies of the seed vApp are created. Therefore, a seed vApp can be used for only one replication.
Creating Seed vApps in the Cloud
Seed vApps on the target cloud site can be created in the following ways.
Offline data transfer: You can export a VM as an OVF package and let a Cloud service administrator import the package in your cloud organization.
Clone a VM: A VM in the org virtual data center can be cloned to create a seed vApp. vCloud Director Extender calculates checksum and exchanges the different blocks from the source VM to the seed vApp.
Copy over the network: A source VM can be copied to the cloud organization by using means other than vCloud Director Extender to transfer source data to the target site.
The size and number of disks, and their assignment to disk controllers and bus nodes must match between the source and the seed VM. For example, if the source VM has two disks of 2 GB each, one of them assigned to SCSI controller 0 at bus number 0, and the second one assigned to SCSI controller 1 at bus number 2, the seed vApp that you use must have the same hardware configuration - 2 disks of 2 GB each, at SCSI 0:0 and at SCSI 1:2.