Metrics being added:
- read_tolerance: No of drive failures that can be tolerated without
disrupting read operations
- write_tolerance: No of drive failures that can be tolerated without
disrupting write operations
- read_health: Health of the erasure set in a pool for read operations
(1=healthy, 0=unhealthy)
- write_health: Health of the erasure set in a pool for write operations
(1=healthy, 0=unhealthy)