Digital BW, The Print

Hi,
I've just got Amadou's book out of the library and he suggests having a separate scratch disk of 80-120 GB. I was told that it only had to be 6x the size of your largest file. 

As mine's only about 500-600MB, my scratch disk is only 3.9GB - and yes, I do get messages saying it's filling up sometimes. ... so I'm thinking of making it 20GB. 

What really is the rule of thumb here?

thanks,
Richard
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