On Aug 23, 10:28, Fred Cisin (XenoSoft) wrote:
> Quick simple puzzle: why would a drive that steps both disks at the same
> time be significantly SLOWER when DISKCOPY'ing a disk than using separate
> drives?
> Hint: MUCH faster when copying if you write software specifically for
it.
Because it will read some number of tracks, stepping inward as it does so,
then have to step back to the correct track to start writing. Example:
read tracks 0 to 19 (20 in total, 19 steps), step back 19 tracks, write 20
tracks (19 steps again); repeat. Total number of steps to copy n tracks is
just less than 3n. If you want to read the tracks back to verify them,
life is even worse, as the total is almost 5n.
On the other hand, if you do it one track at a time: read a track, write
that track, then step forward one track, the total number of steps to copy
n tracks is n-1 steps. And still only n-1 if you verify each track as you
go.
--
Pete Peter Turnbull
Network Manager
University of York
Received on Thu Aug 23 2001 - 16:34:54 BST