How critical is it to stay same brand/model hard drives in RAID?

[jtvang125]

I know size has to be the same throughout the drives but what about between different brands? Say you have a few Samsungs, a few Seagates or Western Digital and they're all 7200 rpm. Would this be ok or is it imperative that they're all the same size, brand and model?

 

[CalvinHobbes]

It doesn't matter which brand they are or model they are. In some cases size doesn't matter but you may waste some space on the larger discs.