Cisco Cat Stack

Priority Values

A higher priority value for a stack member increases its likelihood to be elected stack master and to retain its stack member number. The priority value can be 1 to 15. The default priority value is 1. You can display the stack member priority value with the show switch user EXEC mode command.
3750-Stk>show switch
                                               Current
Switch#  Role      Mac Address     Priority     State
--------------------------------------------------------
 1       Slave     0016.4748.dc80     1         Ready
*2       Master    0016.9d59.db00     5         Ready
Cisco recommends that you assign the highest priority value to the switch that you prefer to be the stack master. This ensures that the switch is re-elected as stack master if a re-election occurs.
How do you change the priority value?
From the global configuration mode, issue the command switch stack-member-number priority new-priority-value .
From the bootloader switch: prompt, issue the command set SWITCH_PRIORITY new-priority-value .
Even though the priority value applies immediately to the member, it will not affect the status of the current stack master. New priority value will play a role in the next stack-master election.
Stack Master Election

How is the stack master elected?
These rules have been defined to determine which unit within a stack is chosen as the master. When switches are added or stacks are merged, the master will be chosen based on these rules, in the order specified:
The switch that is currently the stack master
Note: When stacks merge, the elected stack master would have been the master of one of the merged stacks.
Note: When stacks partition, the stack master of the original stack will be the master of its partition.
The switch with the highest stack member priority value
Note: Cisco recommends that you assign the highest priority value to the switch that you prefer to be the stack master. This ensures that the switch is re-elected as stack master if a re-election occurs.
The switch that uses the non-default interface-level configuration
The switch with the higher Hardware/Software priority. These switch software versions are listed from highest to lowest priority:
Cryptographic IP services image software
Noncryptographic IP services image software
Cryptographic IP base image software
Noncryptographic IP base image software
Note: Switches that run Cryptographic or IP services image will take a longer time to load than Non-Cryptographic or IP base image. When you power on or reset an entire switch stack, some stack members will not participate in the stack master election. This is because stack members that are powered on within the same 20-second time frame participate in the stack master election and have a chance to become the stack master. Stack members that are powered on after the 20-second time frame do not participate in this initial election and only become stack members. At times, switches with lower software priority can become the stack master, but all stack members will participate in the stack master re-election.
The switch with the longest system up-time
The switch with the lowest MAC address
Note: Data forwarding will not be affected within the stack master election.
When is the stack master elected?
When the whole switch stack is reset1
When the stack master is reset or powered off
Note: If you reset the stack master, it would reset the whole stack.
When the stack master is removed from the stack
When the stack master switch has failed
The switch stack membership is increased by if you add powered-on standalone switches or switch stacks.1
1Within these events, the current stack master has a greater chance to get re-elected

Creation and Management of Catalyst 3750 Switch Stacks
http://www.cisco.com/c/en/us/support/docs/switches/catalyst-3750-series-switches/71925-cat3750-create-switch-stks.html

Do I need to configure the priority and switch number, or it doesn't care when I'm using the same model for stacking,

Tks again.

The master already has a higher priority in your stack so no need to change that unless you want to change the master switch.If adding more switches to the stack you would change the priority of the switch you want to set as master to 15.

We will replace all the switch, so do I need to configure the priority for one of the switch first.

Inaddition, does the number assignment related to the physical stack assignment ?

Tks

No, if  you remove the master there will be a re-election .

Remove a Member from the Stack

Complete these steps to remove a member from the stack:
Make sure that the stack is fully connected so that, when you remove the member, the stack will be at least in half connectivity, and do not partition.
Power off the member to be removed.
If the member was the stack master, the stack master election will occur, otherwise no election will occur.
Remove the StackWise cables from the member and close the stack ring.
Issue the command show switch to verify the stack membership.

Is there any cable requirement for stacking up ? Is it normal for port 1 of one switch to connect to port 2 of another switch.

Tks

Tks