Hi,

Consideration would be 5% of VNX Model Capacity.

For more information, Refer VNX Best Practices for Performance Applied Best Practices Guide document from EMC Support site.

Thanks

Madhusudan

I think there is no "simple Ratio", there are some Guidelines but more Important is to know what is my Workload and how Big will be my Working Set. Also for Example, if you have let´s say 99% Write IOPS than FAST Cache is not realy the best Option.

I think the First Step should be, read the Document provided by Ganapa and then provide us more Details about the Workload. Because Storage Sizing ist mostly "it depends".......

I agree with everything that's been stated above.  The ratio depends on what you're trying to do.  However, a good starting point is 5% Flash, 20% SAS, and 75% NL-SAS.  From there you should adjust to fit your needs.

Agree with the above, it always depends on the profile of your workloads and that needs analysis of the performance log. Apply the rule of thumb suggested by briahen if you don't have any idea about the workloads.