suppose it comes down to the process that dataontap uses to decide where to write new data withn the volume (which i dont know in depth)
i assumed that if the LUN was Thin Prov that it may take a 'fraction' longer to allocate / decide on space and the write to the volume ? (maybe nothing in this ??)
although - i presume that if a volume is containing only 1 LUN with vol Frac res set to 0 and that volume is guaranteed to volume then it makes no odds to space if the LUN Thin Provisioned anyway ? (as no other 'activity' would write to, and use the space for, the LUN anyway)