Re: [PLUG] Copying files to multiple volumes

Apologies for the delayed reply. I was busy with election related stuff yesterday, and am still trying to make sense of it. Things would be so much simpler if the answer were 42, or some such…

Extending the heuristic to n drives is straightforward. After sorting the files by size, put the first n files in the first n drives from drive 1 to drive n. Then put the next n files the drives from drive n to drive 1 (i.e., in reverse order). Then put the next n files in drives 1 through n. And so on.

Like any simple-minded heuristic, this has pathological cases. For example, if you have one really big file that takes up most of one drive, and a gazillion small files that together fit onto a second drive, this heuristic can produce pessimal (the opposite of optimal) results. A modified heuristic is to fill each drive till it is as full as the last drive, and add one file to the drive when starting a new row (i.e., to drive 1 or drive n). I'm sure that also has pathological cases, but I have not thought through the problem enough to articulate what those look like.

Regards

– Bhaskar

On Tue, Nov 3, 2020 at 3:03 AM Steve Litt via plug <plug@lists.phillylinux.org> wrote:

On Thu, 29 Oct 2020 10:35:06 -0400
"K.S. Bhaskar via plug" <plug@lists.phillylinux.org> wrote:

> You can of course extend the boustrophedon heuristic to n drives, if
> you have the drives, e.g., largest file on drive 1, next largest on
> drive 2, next two on drive 3, next on drive 2, next two on drive 1,
> etc. And maybe two drives will suffice if you compress each file
> before storing it.

Bhaskar,

Long ago I made a backtracking algorithm (Ruby) to best-fit a bunch of
files onto a bunch of volumes. Can you spell overkill? I like your idea
much better.

SteveT

Steve Litt
Autumn 2020 featured book: Thriving in Tough Times
http://www.troubleshooters.com/thrive
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