Compaq Infortrend 1 ID Mapping Status Normal Operation, 2 ID Mapping Status Controller Failed

Table 10 - 1 ID Mapping Status (Normal Operation)

Channel	ID	Status	Target Chip
0	0 (Primary ID)	Active	Pri. Controller
			channel 0
	1 (Secondary ID)	Standby	Sec. Controller
			channel 0
1	1 (Secondary ID)	Active	Sec. Controller
			channel 1
	0 (Primary ID)	Standby	Pri. Controller
			channel 1

In the event of controller failure (say, the Primary controller fails), the once inactive ID (chip) will become active:

Table 10 - 2 ID Mapping Status (Controller Failed)

Channel	ID	Status	Target Chip
0	0 (Primary ID)	Active	Pri. Controller
			channel 0 – Failed!
	1 (Secondary ID)	Standby- becomes	Sec. Controller
		Active!	channel 0
1	1 (Secondary ID)	Active	Sec. Controller
			channel 1
	0 (Primary ID)	Standby	Pri. Controller
			channel 1- Failed!

Figure 10 - 8 Controller Failover

For every channel that is actively serving I/Os, there is another on the alternate controller that stays idle and will inherit the task should its counterpart fail.

An exception to this is that active IDs may co-exist on single or multiple host channels. As long as I/O bandwidth is not of the concern, then standby chips may not be necessary.

10-10 Infortrend