Webdav verlangsamt backup

       -c, --checksum
              This changes the way rsync checks if the files have been changed and are in need of a trans‐
              fer.  Without this option, rsync uses a "quick check"  that  (by  default)  checks  if  each  
              file’s  size  and  time  of  last  modification match between the sender and receiver.  This
              option changes this to compare a 128-bit checksum for each file that has  a  matching  size.
              Generating the checksums means that both sides will expend a lot of disk I/O reading all the
              data in the files in the transfer (and this is prior to any reading that  will  be  done  to
              transfer changed files), so this can slow things down significantly.

              The  sending side generates its checksums while it is doing the file-system scan that builds
              the list of the available files.  The receiver generates its checksums when it  is  scanning
              for  changed  files,  and will checksum any file that has the same size as the corresponding
              sender’s file:  files with either a changed size or a  changed  checksum  are  selected  for
              transfer.

              Note  that  rsync  always verifies that each transferred file was correctly reconstructed on
              the receiving side by checking a whole-file checksum that is generated as the file is trans‐
              ferred,  but  that  automatic  after-the-transfer  verification  has nothing to do with this
              option’s before-the-transfer "Does this file need to be updated?" check.  

              For protocol 30 and beyond (first supported in 3.0.0), the checksum used is MD5.  For  older
              protocols, the checksum used is MD4.