--chunk & pretend?

Hi,
   I've partitioned 5 drives to create a RAID6. I have a few questions:

1) Is there a 'pretend' option for create? Something that would say
all the things it intended to do but then do nothing?

2) For the uninitiated, what should I be considering about chunk size?
The machine is a home server. It runs a bunch of VMWare and Virtualbox
VMs. The VM's typically result in a few large files. (2GB or larger)
Is the 512K default reasonable for this work model?

Thanks,
Mark