CMM software redundancy is one of the switch’s most important fail over features. For CMM software redundancy, at least two fully-operational switches must be linked together as a stack. In addition, the CMM software must be synchronized. (Refer to “Synchronizing the Primary and Secondary CMMs” on page 5-27 for more information.)
In a stack of switches, one of the switches has the primary role and the other switch has the secondary role at any given time. (The primary and secondary roles are determined by the switch number indicated on the LED on the front panel; the lowest number switch becomes the primary switch in the stack.) The primary switch manages the current switch operations while the secondary switch provides backup (also referred to as “fail over”).
Additional switches in a stack are set to “idle” for the purposes of redundancy. For more information on managing a stack of switches, see the “Managing Stacks” chapter found in the related
OmniSwitch AOS Release 6250/6350/6450 Hardware Users Guide.
When two CMMs are running in a stack, one CMM has the primary role and the other has the secondary role at any given time. The primary CMM manages the current switch operations while the secondary CMM provides backup (also referred to as “fail over”).
Redundancy Scenarios
The following scenarios demonstrate how the CMM software is propagated to other switches in a stack for the purposes of coherent redundancy. In the examples below, W represents the working directory and C represents the certified directory.
Scenario 1: Booting the Stack
The following diagram illustrates what occurs when a stack powers up. The stack displayed is a three- switch stack.
Powering Up a Stack
W C W C W C
1. Stack is pow- ered up and boots from the certified directory.
2. The contents of the certified direc- tory of the primary
CMM switch are copied to the working directory of the secondary CMM switch. The working directory is then copied to the certi- fied directory.
3. The contents of the certified direc- tory of the pri- mary CMM
switch are copied to the working directory of addi- tional switches. The working direc- tory is then copied to the certified directory.
CMM Files Managing CMM Directory Content
This process occurs automatically when the switch boots. The working and certified directory relationship described in the preceding figure in “Software Rollback Feature” on page 5-4 continues to apply to the primary CMM switch.
Generally speaking, the switch assigned the lowest stack number is the primary CMM switch; the switch with the next lowest stack number is the secondary CMM switch, and all other switches are idle. For more information on stack numbering, see the “Managing Stacks” chapter found in the related OmniSwitch AOS Release 6250/6350/6450 Hardware Users Guide.
Scenario 2: Rebooting from the Working Directory
Since changes to the boot.cfg file and new.img files are initially saved to the working directory, sometimes it is necessary to boot from the working directory to check the validity of the new files. The following diagram illustrates the synchronization process of a working directory reboot. The stack displayed is a three switch stack.
Booting from the Working Directory
This synchronization process occurs automatically on a working directory reboot.
Note. It is important to certify the working directory and synchronize the stack as soon as the validity of the software is established. Stacks booted from the working directory or unsynchronized stacks are at risk of mismanaging data traffic due to incompatibilities in different versions of switch software. Certifying the working directory is described in “Copying the Working Directory to the Certified Directory” on
page 5-21, while synchronizing the switch is described in “Synchronizing the Primary and Secondary CMMs” on page 5-27.
W C W C W C
1. Stack is booted up from the work- ing directory.
2. The primary CMM switch cop- ies its working directory to the secondary CMM switch working directory. 3. The primary CMM switch cop- ies its working directory to the other switch work- ing directories.
Managing CMM Directory Content CMM Files
Scenario 3: Synchronizing Switches in a Stack
When changes have been made to the primary CMM switch certified directory, these changes have to be propagated to the other switches in the stack. This could be done by rebooting the stack. However, a loss of switch functionality is to be avoided, a copy flash-synchro command can be issued.
The following diagram illustrates the process that occurs when using a copy flash-synchro command. The stack shown is a three switch stack.
Synchronizing Switches in a Stack
The copy flash-synchro command (described in “Synchronizing the Primary and Secondary CMMs” on page 5-27) can be issued on its own, or in conjunction with the copy working certified command (described in “Copying the Working Directory to the Certified Directory” on page 5-26).
Note. It is important to certify the working directory and synchronize the stack as soon as the validity of the software is established. Stacks booted from the working directory or unsynchronized stacks are at risk of mismanaging data traffic due to incompatibilities in different versions of switch software. Certifying the working directory is described in “Copying the Working Directory to the Certified Directory” on page 5-21, while synchronizing the switch is described in “Synchronizing the Primary and Secondary CMMs” on page 5-27. W C W C W C 1. A copy flash- synchro com- mand is issued on the primaryCMM switch. 2. The contents of the certified direc- tory of the primary CMM switch are copied to the working directory of the secondary CMM switch. The working directory is then copied to the certi- fied directory.
3. The contents of the certified direc- tory of the pri- mary CMM switch are copied to the working directory of additional switches. The working directory is then copied to the certified direc- tory.
CMM Files Managing CMM Directory Content
Scenario 4: Adding a New Switch to a Stack
Since the OmniSwitch is designed to be expandable, it is likely that new switches are added to stacks. The stack automatically detects new switches added to the stack, and new switches can pass traffic without a complete reboot of the stack.
However, a new switch added to the stack may not have the same software as the rest of the stack. In this case, the new switch must be synchronized with the stack software.
The following diagram illustrates this idea. The diagram shows a stack of three switches to which a fourth switch is added.
Synchronizing a Stack with Three More Switches
W C W C W C W C
1. Stack is pow- ered up and boots from the certified directory, or a copy flash- synchro com- mand is issued.
2. The contents of the certified direc- tory of the primary
CMM switch are copied to the working directory of the secondary CMM switch. The working directory is then copied to the certi- fied directory.
3. The contents of the certified direc- tory of the pri- mary CMM switch are copied to the working directory of additional switches. The working directory is then copied to the certified direc- tory.
4. In a stack of four or more switches the sec- ondary CMM switch assists in the synchroniza- tion process, after it has been syn- chronized with the primary CMM switch.
Managing CMM Directory Content Managing the Directory Structure (Non-Redundant)