topic Re: Deliberately creating file fragmentation in Operating System - OpenVMS

Deliberately creating file fragmentation

John A. Beard — Tue, 06 Nov 2007 10:58:42 GMT

Hi folks,

Does anyone have a simple DCL script that I can use to create multiple file fragments on an ODDS-2 disk. We are wanting to run this on a scratch disk that we can test Raxco's PerfectDisk against. I saw something similar here a long time ago, but I have had no success in locating it so far.

Thanks.. John

Re: Deliberately creating file fragmentation

Karl Rohwedder — Tue, 06 Nov 2007 11:14:11 GMT

A very simple script:

$ open/wr l1 a.dat
$ open/wr l2 b.dat
$ i=0
$1:
$ i=i+1
$ write l1 "datensatz"
$ write l2 "datensatz"
$ if (i.lt.1000000) then $ goto 1
$ close l1
$ close l2

creates 2 interleaved files, can easily be extended...

regards Kalle

Re: Deliberately creating file fragmentation

John A. Beard — Tue, 06 Nov 2007 11:54:40 GMT

Thanks..... I will deploy it now.

Re: Deliberately creating file fragmentation

Jon Pinkley — Tue, 06 Nov 2007 13:15:01 GMT

If you are planning to compare this to another product, or even the different optimization levels of Perfect Disk, I would recommend making a physical backup of the "fragmented" disk, so you will be able to restore it to a known state when tying another option.

Which version of PerfectDisk and which platform are you doing your testing on?

Re: Deliberately creating file fragmentation

Hein van den Heuvel — Tue, 06 Nov 2007 13:29:55 GMT

Before running this, or something like this, make sure to de-optimize the RMS settings.
Check your cluster size.
Check the dis default extent
$ SET RMS/EXT=<1-cluster>
$ SET RMS/BLOC=<1/2 cluster>

Be sure to write/sym a good long string ( F$FAO(!1000*x) )
Add a 3rd file to be deleted to validate fragmented free space work.
Add still more files every so many records.

But really... how realistic will any such trivial test be? Can you clone a real application disk? Will files be opened/closed during defrag tests?

Cheers,
Hein.