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Unless there is something else, unusual, about your system my recommendation would be that you stay with the default 1MB.
This is not dissimilar from the theoretical gains to be had from changing the default block size from 8K. Perhaps in some rare system it helps but usually it just introduces the DBA team to creating more SRs due to finding bugs.
Thanks Dan. I suspected as much due to the absence of info out there on this particular topic. I hear you on the comparsion with deviating from a tried-and-true standard 8K Oracle block size. Probably not worth the hassle. I don't know of any particular justification with this system to bump up the AU size--especially if this is an esoteric and little-used technique. The only justification is official Oracle documentation suggesting the value change. Since it seems you can't change an ASM Diskgroup's AU size once you create it, and since we won't have time to benchmark using different AU sizes, I would prefer to err on the side of caution--e.g. first do no harm.
Does anyone out there use something larger than a 1MB AU size? If so, why? And did you benchmark between the standard size and the size you chose? What performance results did you observe?