We had this when they phased out the 450GB 15k drives, all replacements were 600GB and on our T800 that meant 4x600GB in a Mag for every 450GB drive failure (yay free upgrade
).
For us 450/600 on a 15k drive matched well with our IOPs/GB load and as the difference wasn't huge it didn't cause many issues (apart from when the 450s all filled up
).
The 3PAR seemed to slightly weigh the distribution towards the bigger drives in the CPG so we were typically hitting ~90% total array used before the 450s filled, which is not a good place to be in any thin array and was mostly down to delays in our internal order processes.
If the replacements were double or more the original drives it would be more of an issue (I'd look at CPG filters then and maybe tiering the smaller drives as a 'better' tier then the bigger ones, IOs per GB wise).