Why is restore so slow?

[Jerry Aguirre]

Those familiar with using dump and restore will have noticed the
difference in speed between them.  The dump procedure, expecially with
the current multi-buffered version, usually sings along at close to full
tape speed.  Restore, on the other hand, is a real dog taking up to 10
times as long for the same amount of data.

Has anyone done any evaluations of why there is such an extreem
difference in speed?  Granted that creating files involves more overhead
than dumping them restore still seems very slow.  As restore operates on
the mounted file system it has the advantage of accessing a buffered
file system with write behind.

My particular theory is that the disk buffering algorithms are precisely
wrong for restore.  By this I mean they keep in the buffers the data
that will never be needed again and flush the data that will.  I plan to
do some experimentation and would appreciate hearing any ideas you might
offer.

				Jerry Aguirre