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DFG and SETFILENOMOVE

 
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Jim Geier_1
Regular Advisor

DFG and SETFILENOMOVE

I manage an OpenVMS Alpha 8.3 cluster for which we very seldom get scheduled downtime (once or twice per year). The cluster is made up of 3 AlphaServer ES45 systems and they run on a single host-based shadowed system disk.

We have purchased licenses for DFG, and would like to install the software to defragment several non-database disks. The requirement to run the SETFILENOMOVE DCL script against the system disk before installing DFG is delaying our installation by months.

How critical is running SETFILENOMOVE if one is absolutely not going to defragment the system disk? Does DFG work on the system disk beind the scenes without my explicitly telling it to do so?
4 REPLIES
Volker Halle
Honored Contributor
Solution

Re: DFG and SETFILENOMOVE

Jim,

if DFG is not used to defrag the system disk, there is no requirement to run SETFILENOMOVE.

If you need additional confirmation, you could also have a look at that procedure and verify, that all files referenced in that procedure are actually already set nomove on your system disk.

Volker.
Hein van den Heuvel
Honored Contributor

Re: DFG and SETFILENOMOVE

>> The requirement to run the SETFILENOMOVE DCL script against the system disk before installing DFG is delaying our installation by months.

I'm guessing that this delay is purely for non-technical reasons right?

If there is a technical reason, then please explain!

It is perhpas believed, possibly due to a severe lack of understanding, that you need 'approval' for such major command huh?

Could one mark those files no-move, install DFG, and then, unmark the files, prommising never to run DFG against the system disk?

Have you considered alternatives against defragging, notably re-structuring directories and (virtual) devices such that little come and go files do not mix with large and steady?
Maybe use the storage to carve out a few smaller units for quick & dirty stuff, or use the LDdriver to slice a zone from a disk?

hth,
Hein van den Heuvel
Jim Geier_1
Regular Advisor

Re: DFG and SETFILENOMOVE

The delay is that (according to the instructions) SETFILENOMOVE must be executed against the system disk with all systmes accessing the system disk down. And, we are only allowed scheduled downtime rarely -- under normal circumstances, the system is used 24 hours per day.

John Gillings
Honored Contributor

Re: DFG and SETFILENOMOVE

Jim,

SETFILENOMOVE is a fairly innocuous procedure - even though it touches system files. It's perfectly safe to run it, worst case is it will fail to set the NOMOVE bit on files which are locked. It can't upset any running processes.

I'd suggest you just run SETFILENOMOVE and watch for errors. Check any files which report a SET failure - it's possible they're already set to NOMOVE (I think it's done as part of an installation or upgrade).

You'll then know exactly what needs setting, and can reasonably judge the risks. (indeed, if a file is open all the time, or frequently enough that you can't find a window to execute a SET FILE/NOMOVE against it, then any attempt by DFG to defrag that file will also fail).

> absolutely not going to defragment the
> system disk?

Famous last words!

I would strongly recommend AGAINST installing DFG without running SETFILENOMOVE, regardless of any intention to not run DFG on the system disk. Having seen some cases of system disk scrambling due to incorrect defragging (by products other than DFG), it's not pretty and you really don't want to take that risk.
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