1. A method for performing backup of virtual machine data to a target datastore, the method comprising: intercepting, by a backup computing device comprising a volatile memory and nonvolatile storage that is different from the target datastore, a plurality of calls made by a backup process to create a backup of one or more virtual machine disks to the target datastore, the one or more virtual machine disks comprising a plurality of data blocks, the plurality of intercepted calls comprising: (1) at least one open call programmed to open a proxy backup file at a first destination location on the nonvolatile storage of the backup computing device, and (2) at least one write call programmed to write a proxy backup copy of each of the one or more virtual machine disks to the proxy backup file at the first destination location on the nonvolatile storage of the backup computing device; for each intercepted open call, the backup computing device substituting the open call with at least a second open call programmed to open a sparse file at the first destination location; for each intercepted write call, the backup computing device substituting the intercepted write call with at least a second write call, wherein the at least the second write call is programmed to: transfer the data block associated with the particular intercepted write call to the volatile memory of the backup computing device without writing the data block to the nonvolatile storage of the backup computing device; and redirect the data block stored in the volatile memory to a second destination location on the target datastore that is different than the first destination location on the nonvolatile storage of the backup computing device, wherein the redirecting occurs without writing the data block to the nonvolatile storage of the computing device; intercepting a call to close the proxy backup file; and substituting, for the intercepted close call, a call programmed to close the second destination location on the target datastore.