EMC recommends no more than four connectrix switches per fabric based on the following formulae:
| One Switch | Two Switch | ||
|---|---|---|---|
| 32 | Total ports | 64 | Total ports |
| - 4 | ports reserved for card failure | - 4 | ports reserved for card failure |
| 28 | ports remaining. | - 4 | ports reserved for E_ports |
| - (int(28/5)) | No more than 4:1 ratio, hosts : fa | 56 | ports remaining. |
| 23 | Possible host connections | - (int(56/5)) | No more than 4:1 ratio, hosts : fa |
| / 2 | to support multi-pathing | 45 | Possible host connections |
| 11 | total host connections | / 2 | to support multi-pathing |
| 22 | host connections (gain of 11) | ||
| Three switches | Four switches | ||
| 96 | total ports | 128 | total ports |
| - 4 | ports reserved for card failure | - 4 | ports reserved for card failure |
| - 12 | ports reserved for E_ports | - 24 | ports reserved for E_ports |
| 80 | ports remaining | 100 | ports remaining |
| - (int(80/5)) | No more than 4:1 ratio, hosts : fa | - (int(100/5)) | No more than 4:1 ratio, hosts : fa |
| 64 | Possible host connections | 80 | Possible host connections |
| / 2 | to support multi-pathing | / 2 | to support multi-pathing |
| 32 | host connections (gain of 10) | 40 | host connections (gain of 8) |
Putting in that fourth connectrix means that you gain only 8 host connections from a 32 port connectrix switch. At EMC prices, that's going to be a hard sell to the resident bean counters
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