VMware Incremental backups with Accelerator enabled are shown in the Activity Monitor and reports as having the same size as full backups, even though the file count will be much smaller, reflecting only the files that have changed since last backup.
With Accelerator enabled, VMware Incremental backups will store a full backup image on back-end storage while storing only the changed file list in the catalog. This improves VM restore performance as only one image is read during the restore process - as opposed to Full VM restores from non-Accelerator backups which have to process a chain of backup images from the last Full and all subsequent Incrementals). This also conserves disk space for the image catalog by storing only the changed files list.
Therefore, the size of an incremental backup being reported the same as for a full backup reflect the actual image size on back-end storage. Due to back-end de-duplication required by the Accelerator, this figure does not reflect actual disk space occupied by the image.
Note: When you duplicate one of these Accelerator enabled VMware Incremental backups to tape, these images will be rehydrated to Full images and will consume more tapes.
This is by design.