from performance vs rg size to new topic: rg size uniformity within the aggregate

Unfortunately, I've not been enlightened as to performance numbers for varying small aggregate sizes with one raid group, so I guess I'll have to be content with shooting in the dark by starting out small and growing from there if the performance is too lousy. Regardless, may comments were still helpful and they are much appreciated.

But now to a tangentially related subject:

From recent posts, one might be led to believe that it really doesn't

matter much at all what the sizes of your raid groups are within an aggregate. One might get the idea that an aggregate with, say, 3 raid groups of size 6, 12 and 18 wouldn't perform much differently than one with 3 identical raid groups of size 12 because what matters far more than anything else is the data disk count of an aggregate:

For instance:

"...there is no reason one 4+2 and two 16+2s cant perform quite well. There is no unreasonable penalty to doing so ... if the right tools are used to manage it."

"Performance of an aggregate is the total sum of spindles across the entire aggregate."

And

"Forget parity as a limitation to system performance"

However, NetApp's recommendations on raid group sizing within the aggregate might lead one to believe somewhat the opposite:

From http://communities.netapp.com/thread/1587 :

"the recommended sizing approach is to establish a RAID group size that ... achieves an even RAID group layout (all RAID groups contain the same number of drives). If multiple RAID group sizes achieve an even RAID group layout, NetApp recommends using the higher RAID group size value within the range."

and

"Drive deficiencies should be distributed across RAID groups so that no single RAID group is deficient more than a single drive."

That is, NetApp took the time and trouble to say:

1. RAID group sizes within an aggregate shouldn't vary by more than 1 disk 2. Larger RAID group sizes are better (up to a point)

Which runs rather strongly against the grain of what's been said recently in this forum. Can anyone shed more light on this topic?

For instance, what are the drawbacks (and how bad are they) to, say, adding a 6-disk raid group to an aggregate consisting of one 16-disk raid group (instead of spilling for way more disk space than you might need by forking over for the full 16 disks necessary to even things out?).

Thanks Randall