Hi Tomas,
I think 85% is the "magic" number.
If you look at the Redbook: Performance and Best Practices Guide for IBM Storage Flash System and IBM SAN Volume Controller, this occurs several times:
- For best performance results, plan to operate your storage system with ~85% or less physical capacity used. Flash drives depend on free pages being available to process new write operations and to quickly process garbage collection
If you are using data reduction, then regardless of the technology that you choose, it is a best practice to keep the system below ~85% to allow it to respond to sudden changes in the rate of data reduction (such as host encryption being enabled).
For optimal performance and safety,the recommendation is to use the DRP to a maximum of 85%.
Monitor the array’s free space and avoid filling it up with more than 85% of physical capacity.
Your pool should be no more than 85% occupied