Filer_Action Timings                                      J.R.Sutton 17/1/92
--------------------
Reported fault was slow slow copying to or from dos floppy disc.

Observed problem was that the blocksize reduction algorithm to ensure good
desktop response was reducing the blocksize so far that the overall data
transfer rate was very poor.

Fix was to measure the data transfer rate and to increase the target time
for each transfer if the transfer rate reduces below a given fraction of the
initial transfer rate (4K blocksize). This causes it to aim for a larger
blocksize, improving the overall transfer rate.

Measured results
----------------
  Average time taken to copy a 64K file:

        from    to      before change   after change    comment
       --------------------------------------------------------
       scsihd  scsihd       0.74s          0.87s    slightly worse (constant time?)
       scsihd  adfsfd       4.92s          4.88s
       scsihd   doshd       1.46s          1.51s
       scsihd   dosfd      22.94s         10.20s    much better
       adfsfd  scsihd       4.36s          4.39s
       adfsfd  adfsfd        -              -
       adfsfd   doshd       4.84s          5.12s
       adfsfd  adfsfd        -              -
        doshd  scsihd       0.88s          0.95s
        doshd  adfsfd       5.08s          4.93s
        doshd   doshd       1.51s          1.33s
        doshd   dosfd      23.81s         10.97s    much better
        dosfd  scsihd       7.48s          7.31s
        dosfd  adfsfd        -              -
        dosfd   doshd       8.38s          9.33s
        dosfd   dosfd        -              -
       scsihd  econet      19.34s         21.34s
       econet  scsihd      15.36s         14.50s
       scsihd     nfs       2.59s          2.54s
          nfs  scsihd       1.09s          1.22s


  Time taken to copy a 1024K file (1 trial only)
       scsihd  scsihd       3.9s           4.0s
       scsihd   doshd      10.4s          10.0s
        doshd  scsihd       4.2s           4.3s
       scsihd     nfs      28.6s          33.5s
          nfs  scsihd       7.5s           7.3s

I conclude that the worst-case performance is much better at the cost of slightly
increased shortest file copy time.

