The major benefits of having more cache are not hard to understand — applications can run faster, and more capacity can be configured in an storage system without sacrificing performance.
If you check the IBM recommendation(EMC don't really follow the IBM "rule of thumb" for cache-to-backstore ratio) they recommend:
.01 — Ultra-High Performance
.005 — High Performance
.0025 — Moderate Performance
You could also work with specialist to plan to get the required levels of performance by modelling proposed configurations using Disk Magic.
Below spreadsheet shown the recommended Cache memory required for the amount of capacity the storage system will manage.
Minimum Recommended System Memory (GB)
| Useable Capacity (TB) |
Minimum Recommended System Memory (GB) | ||||
| Open and System i | | ZOS | | Both | |||
| High Performance | Standard Performance | High Performance | Standard Performance | Low Access or Archival | |
| Up to 5 TB | 16 GB | 16 GB | 32 GB | 16 GB | 16 GB |
| 5 TB to 11 TB | 32 GB | 16 GB | 64 GB | 32 GB | 16 GB |
| 11 TB to 23 TB | 64 GB | 32 GB | 128 GB | 64 GB | 16 GB |
| 23 TB to 51 TB | 128 GB | 64 GB | 256 GB | 128 GB | 32 GB |
| 51 TB to 118 TB | 256 GB | 128 GB | - | 256 GB | 64 GB |
| 118 TB to 168 TB | - | 256 GB | - | - | 128 GB |
