Allied Telesyn International Corp TurboStack AT-S6 User's Guide download pdf (Page 62)

Fault Tolerance

Voting During the voting process, the master polls each installed module and

examines the stored conﬁguration data.

The master declares the conﬁguration data that is stored on the greatest

number of modules as the correct data, that is, the majority rules. For

example, if data set A exists on modules 1, 3, and 4, and data set B exists

on module 5, the management agent accepts data set A to be correct and

adopts this set of conﬁguration data for subsequent use.

However, a dilemma occurs when there are only two modules installed in

the chassis. In this case, there is no way to determine which data set is

correct. The system defaults to the master data set, which might not be

correct—you may need to reconﬁgure when swapping a spare into the

master position of a two-module department concentrator.

Reconﬁguration is not necessary if you follow the swapping procedure.

Swapping

Modules to Retain

Conﬁguration Data

Conﬁguration data is always retained if module swapping occurs with

power applied, that is, as long as one module remains powered up

throughout the hot swapping procedure. This will cause the use of the

proper data set based upon clock comparison as described above.

If you must remove power for any reason, you perform the swap by either

of the following methods (these steps are only necessary in a two-module

department concentrator).

Method one:

1. Pull out the old master.

2. Place the old backup into the master slot position.

3. Install the spare module in the backup position.

The data set of the old backup is used.

Method two:

1. Pull out the old master.

2. Place the spare module below the old Backup, making the old Backup

the new master.

The spare module becomes the new backup.

Limitations exist when massive chassis reconﬁgurations occur. If all

modules boot at the same time, the voting process occurs. If many modules

have been swapped all at once, incorrect data could be used. If, for

example, several modules had previously been installed together in a

different chassis, they would all vote the same way and their (incorrect)

data might be used. You can avoid this by:

❑ Making configuration changes incrementally, or

❑ Keeping backplane power on so that the master never needs to ask

for a vote

With a standalone hub, however, there is not much the software can do

when this single unit is swapped with a spare because there is no backup.

You must reconﬁgure in this case. Note that the software allows you to

reset the hub conﬁguration to manufacturing defaults.

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Allied Telesyn International Corp TurboStack AT-S6 User's Guide Page 62

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