david wrote:
That's how I understand it also. It will write twice the amount of data to the 4TB than the 2TB, causing the 4TB to be loaded more until it is rebalanced based on hot cold data.
Wrong!
On the HP EVA systems and possibly others, they would fill drives equally percent-wise. The 3PAR will fill (given that there isn't a hardware imbalance) GB for GB(or more exact chunklet for chunklet).
If you fill the drives percent-wise, you will end up with a scenario that your 2x sized drives will always handle 2x the IOPS... which most people understand is bad. With 3PAR you even the load up to the point where the smallest drives are full. From that point on, all new writes will only hit the larger drives wit free capacity and as you add more data to the larger drives the IOPS imbalance will increase.
It's simple math. The 3PAR will wide-stripe and the important factor will be IOPS per GB. And with wide-striping the data will be distributed across all drives and you will get in a state where the drives with the lowest IOPS per GB will limit the rest of the tier/cpg. <insert cheesy saying about weakest link/slowest drive>