My company recently deployed FAST-VP on a V-Max 10K using 3 disk pools, EFD, FC and SATA.

After running FAST-VP for 8 months it's apparent that the FAST controller over weights the higher tiers of disk (i.e. EFD and FC).

Our EFD pool is always above 95% utilized, which is good, our FC pool hovers around 70% utilized and SATA around 30%.

So my question is at what level of FC pool utilization should we be planning to add more disk? 75%, 80%, 85%?

It seems like the FAST controller is demoting from the FC tier, to the SATA tier in order to avoid running out of space.

We don't want to get into a situation where we're demoting data because we HAVE to, we only want to demote to SATA when the data is truly cold.

Thanks.