To back up machines in an ESXi Free environment, regular Acronis Agent for Windows/Agent for Linux (as opposed to Acronis Agent for ESX/ESXi or Acronis Agent for VMware) should be installed inside the virtual machines. Agentless backup is not supported.
Acronis Backup Cloud uses Resumable Backup technology for disk-level, file-level and application-level backups of all systems(except ESXi configuration backup). This technology reduces network load and therefore enhances backup performance.
Resumable Backup means that in case of a backup failure data upload will be resumed, i.e.:
Replication is creating backups in multiple locations with a single backup plan. This feature allows replicating backups from a local/network storage to multiple local/network storage, to Acronis cloud, or to an on-premises cloud based on Acronis storage (applicable to Acronis Backup Cloud).
Acronis services to use for upload and download of large amounts of data to cloud
Backing up and restoring large amounts of data to a cloud storage over a slow Internet connection is time-consuming. To help backup service users in these cases, we at Acronis have designed special services for initial upload and download of large amounts of data. These services help end users save time and network traffic by sending the data to the cloud data center on a hard drive or request a hard drive with their backups from the data center.