How to stop LLT and GAB in VCS

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How to stop LLT and GAB in VCS

In this article we are going to understand how to stop LLT and GAB in VCS properly and start them and verify cluster status.This may be needed as part of troubleshooting effort while investigating issues in cluster.So let us understand briefly what is LLT and GAB and what is their role in VCS.

What is LLT

LLT is basically transport layer protocol used to transmit heartbeats between cluster nodes.It stands for low latency transport . LLT helps GAB to determine state of the node in cluster.It helps in inter system communication traffic equally  among all nodes.Including high and low priority links total 8 LLT links can be created.

LLT status of cluster can be verified using below command.Output is truncated.

[[email protected]]# lltstat -nvv |more
LLT node information:
    Node                 State      Link      Status      Address
   * 0 linsrv01        OPEN       eth2      UP           2C:76:8A:56:81:C2
                                          eth3      UP           2C:76:8A:56:81:C3
     1 linsrv02        OPEN
                                            eth2       UP          2C:76:8A:56:85:3F
                                            eth3       UP          2C:76:8A:56:85:3E

What is GAB

GAB is used for group membership services and atomic broadcast.IT maintains cluster membership tracking heartbeat over LLT. If there is no heartbeat over LLT GAB broadcast info to I/O fencing to take further action.It is named as GAB due to Group membership and ATOMIC Broadcast.

GAB membership can be displayed using below command.

[[email protected]]# gabconfig -a
GAB Port Memberships
===============================================================
Port a gen   7d6003 membership 01
Port h gen   7d6007 membership 01

So now we have some details about LLT and GAB.These service cab be restarted and started back with below sequence of commands .This will be proper way how to stop llt and gab in vcs.

Stopping LLT/GAB

# /sbin/gabconfig –U                               # Unconfigure GAB
# /sbin/lltconfig –U                                 # Unconfigure LLT
# modinfo |egrep “gab|llt”                   # To determine Ids of GAB/LLT modules.
# modunload –i 305                                # Unload GAB modules.
# modunload –i 292                                # Unload LLT modules.

Starting LLT/GAB

# /etc/rc2.d/S70llt start                           # Restart LLT
# /etc/rc2.d/S92gab start                         # Restart GAB
# hastart                                                  # Start Cluster

VCS Status Validation

# /sbin/gabconfig –a                      # Verify GAB & VCS are Started
# /sbin/gabconfig -a                      # To display link config info.
# vxdctl -c mode                          # Finds master node when CVM is running
# cat /etc/llttab                            # To verify LLT configuration
# lltstat -n                                    # To verify that links are active for LLT.
# lltstat -p                                    # To obtain info about ports open for LLT.

If above method is not working in scenario if one of your node is having critical hardware kind of issues and you do not have enough node to run cluster you can do same using seed number.

Starting and Stopping LLT

# /sbin/gabconfig –c –n                  # Seed number 
# /sbin/gabconfig –U                     # Starting and Stopping GAB
# /sbin/gabdiskhb –l                      # Gab Config

LLT Status/Verification

# /sbin/lltconfig –a list lltstat|lltshow|lltdump               
# hatype –modify                           
# hasys –force system_name          
# hauser –add user_name              
# hacf –verify 

So finally you can check cluster status using below.Still problem not resolve keep troubleshooting ….

# hastatus –sum  

That,s it related to how to stop llt and gab in vcs troubleshooting effort.Thank you very much for going through above mentioned steps.

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RSY Digital World

RSY Digital World Founder & [email protected] Digital World. A UNIX Linux expert having a more than 20 years of experience in Solaris Red Hat Linux HP-UX AIX Unixware Open Server Veritas Storage Cloud Bigdata and many more in UNIX LINUX Infrastructure technologies.

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