Is it OK to perform other tasks during defragment?

AddRAM said:

Your disk/disks should always be 0% fragmented, that should determine how often you run it.

...if it should be 0%, then that may be why I have been told to do it once every 2 or 3 weeks? .... the defragment itself says "10%"?

If there's persistent fragmentation after defrag, try boot time defrag to get System files.

I'm not sure 0 is a realistic goal and would like to hear more opinion about it.

Often it's large ISO's so what is the efficacy of defragging those?

Newcomer7 said:

...if it should be 0%, then that may be why I have been told to do it once every 2 or 3 weeks? .... the defragment itself says "10%"?

If you are using Windows defragger on a schedule and are concerned, you could do a manual defrag to get the defragmentation percentage down to 0. Then set the schedule for weekly automated defrag and take a look at defrag percentage every few weeks to see if it's moving up significantly from 0. Mine is rarely other than 0.

I've NEVER noticed performance degradation from fragmentation, even in the days prior to automated scheduling, when I would occasionally see defrag percentages in the 15 to 20 range if I forgot about manual defrag for months.

To be honest, I don't see any difference before and after defrag (at 1%). I just do it for the sack of it

I never reach that level.... the highest I can remember was about 3% even if I had not defrag it for ages...