VERITAS CLUSTER SERVER (VCS) INTERVIEW QUESTIONS & ANSWERS

1. Question 1. What Are The Different Service Group Types?

   Answer :

   Service groups can be one of the 3 type :

   1. Failover – Service group runs on one system at a time.
   2. Parallel – Service group runs on multiple systems simultaneously.
   3. Hybrid – Used in replicated data clusters (disaster recovery setups). SG behaves as Failover within the local cluster and Parallel for the remote cluster.

    

2. Question 2. Where Is The Vcs Main Configuration File Located ?

   Answer :

   The main.cf file contains the configuration of the entire cluster and is located in the directory /etc/VRTSvcs/conf/config.

    




3. Question 3. How To Set Vcs Configuration File (main.cf) Ro/rw ?

   Answer :

   To set the configuration file in read-only/read-write :

   • # haconf -dump -makero     (Dumps in memory configuration to main.cf and makes it read-only)
   • # haconf -makerw           (Makes configuration writable)

    

4. Question 4. Where Is The Vcs Engine Log File Located ?

   Answer :

   The VCS cluster engine logs is located at /var/VRTSvcs/log/engine_A.log. We can either directly view this file or use command line to view it:

   # hamsg engine_A

    




5. Question 5. How To Check The Complete Status Of The Cluster?

   Answer :

   To check the status of the entire cluster :

   # hastatus -sum

    




6. Question 6. How To Verify The Syntax Of The Main.cf File?

   Answer :

   To verify the syntax of the main.cf file just mention the absolute directory path to the main.cf file :

   # hacf -verify /etc/VRTSvcs/conf/config

    

7. Question 7. What Are The Different Resource Types?

   Answer :

   • Persistent : VCS can only monitor these resources but can not offline or online them.
   • On-Off : VCS can start and stop On-Off resource type. Most resources fall in this category.
   • On-Only : VCS starts On-Only resources but does not stop them. An example would be NFS daemon. VCS can start the NFS daemon if required, but can not take it offline if the associated service group is take offline.

    




8. Question 8. Explain The Steps Involved In Offline Vcs Configuration?

   Answer :

   • Save and close the configuration :
     # haconf -dump -makero
   • Stop VCS on all nodes in the cluster :
     # hastop -all
   • Edit the configuration file after taking the backup and do the changes :
     # cp -p /etc/VRTSvcs/conf/config/main.cf /etc/VRTSvcs/conf/config/main.cf_17march
     # vi /etc/VRTSvcs/conf/config/main.cf
   • Verify the configuration file syntax :
     # hacf -verify /etc/VRTSvcs/conf/config/
   • start the VCS on the system with modified main.cf file :
     # hastart
   •  start VCS on other nodes in the cluster.

   Note : This can be done in another way by just stopping VCS and leaving services running to minimize the downtime. (hastop -all -force GAB, LLT and HAD)

    

9. Question 9. What Is Gab, Llt And Had And What's Their Functionalities ?

   Answer :

   GAB, LLT and HAD forms the basic building blocks of vcs functionality:

   • LLT (low latency transport protocol) – LLT transmits the heartbeats over the interconnects. It is also used to distribute the inter system communication traffic equally among all the interconnects.
   • GAB (Group membership services and atomic broadcast) – The group membership service part of GAB maintains the overall cluster membership information by tracking the heartbeats sent over LLT interconnects. The atomic broadcast of cluster membership ensures that every node in the cluster has same information about every resource and service group in the cluster.
   • HAD (High Availability daemon) – the main VCS engine which manages the agents and service group. It is in turn monitored by a daemon named hashadow.

    




10. Question 10. What Are The Various Gab Ports And Their Functionalities ?

    Answer :

    • a : gab driver
    • b : I/O fencing (to ensure data integrity)
    • d : ODM (Oracle Disk Manager)
    • f  : CFS (Cluster File System)
    • h : VCS (VERITAS Cluster Server: high availability daemon, HAD)
    • o : VCSMM driver (kernel module needed for Oracle and VCS interface)
    • q : QuickLog daemon
    • v : CVM (Cluster Volume Manager)
    • w : vxconfigd (module for cvm)

     

11. Question 11. How To Check The Status Of Various Gab Ports On The Cluster Nodes?

    Answer :

    To check the status of GAB ports on various nodes :

    # gabconfig -a

     




12. Question 12. Whats The Maximum Number Of Llt Links (including High And Low Priority) Can A Cluster Have ?

    Answer :

    A cluster can have a maximum of 8 LLT links including high and low priority LLT links.

     




13. Question 13. How To Check The Detailed Status Of Llt Links ?

    Answer :

    The command to check detailed LLT status is :

    # lltstat -nvv

     

14. Question 14. What Are The Various Llt Configuration Files And Their Function ?

    Answer :

    LLT uses /etc/llttab to set the configuration of the LLT interconnects.
    # cat /etc/llttab
    set-node node01
    set-cluster 02
    link nxge1 /dev/nxge1 - ether - -
    link nxge2 /dev/nxge2 - ether - -
    link-lowpri /dev/nxge0 – ether - -

    Here, set-cluster -> unique cluster number assigned to the entire cluster [ can have a value ranging between 0 to (64k – 1) ]. It should be unique across the organization.

    set-node -> a unique number assigned to each node in the cluster. Here the name node01 has a corresponding unique node number in the file /etc/llthosts. It can range from 0 to 31.

    Another configuration file used by LLT is – /etc/llthosts. It has the cluster-wide unique node number and nodename as follows:

    # cat /etc/llthosts
    0 node01
    1 node02

    LLT has an another optional configuration file : /etc/VRTSvcs/conf/sysname. It contains short names for VCS to refer. It can be used by VCS to remove the dependency on OS hostnames.

     

15. Question 15. What Are Various Gab Configuration Files And Their Function ?

    Answer :

    The file /etc/gabtab contains the command to start the GAB.

    # cat /etc/gabtab
    /sbin/gabconfig -c -n 4

    here -n 4 –> number of nodes that must be communicating in order to start VCS.

     




16. Question 16. How To Start/stop Gab?

    Answer :

    The commands to start and stop GAB are :

    # gabconfig -c        (start GAB)
    # gabconfig -U        (stop GAB)

     

17. Question 17. How To Start/stop Llt?

    Answer :

    The commands to stop and start LLT are :

    # lltconfig -c       -> start LLT
    # lltconfig -U       -> stop LLT (GAB needs to stopped first)

     




18. Question 18. What’s A Gab Seeding And Why Manual Gab Seeding Is Required ?

    Answer :

    The GAB configuration file /etc/gabtab defines the minimum number of nodes that must be communicating for the cluster to start. This is called as GAB seeding.

    In case we don’t have sufficient number of nodes to start VCS [ may be due to a maintenance activity ], but have to do it anyways, then we have do what is called as manual seeding by firing below command on each of the nodes.

    # gabconfig -c -x

     




19. Question 19. How To Start Had Or Vcs ?

    Answer :

    To start HAD or VCS on all nodes in the cluster, the hastart command need to be run on all nodes individually.

    # hastart

     

20. Question 20. What Are The Various Ways To Stop Had Or Vcs Cluster ?

    Answer :

    In general, to add a service group named SG with 2 nodes (node01 and node02) :

    • haconf –makerw
    • hagrp –add SG
    • hagrp –modify SG SystemList node01 0 node02 1
    • hagrp –modify SG AutoStartList node02
    • haconf –dump -makero

     




21. Question 21. How To Check The Configuration Of A Service Group – Sg ?

    Answer :

    To see the service group configuration :

    # hagrp -display SG

     

22. Question 22. How To Bring Service Group Online/offline ?

    Answer :

    To online/offline the service group on a particular node :

    # hagrp -online [service-group] -sys [node]      (Online the SG on a particular node)

    # hagrp -offline [service-group] -sys [node]        (Offline the SG on particular node)

    The -any option when used instead of the node name, brings the SG online/offline based on SG’s failover policy.

    # hagrp -online [service-group] -any

    # hagrp -offline [service-group] -any

     

23. Question 23. How To Switch Service Groups ?

    Answer :

    The command to switch the service group to target node :

    # hagrp -switch [service-group] -to [target-node]

     




24. Question 24. How To Freeze/unfreeze A Service Group And What Happens When You Do So ?

    Answer :

    When you freeze a service group, VCS continues to monitor the service group, but does not allow it or the resources under it to be taken offline or brought online. Failover is also disable even when a resource faults. When you unfreeze the SG, it start behaving in the normal way.

    To freeze/unfreeze a Service Group temporarily :

    # hagrp -freeze [service-group]
    # hagrp -unfreeze [service-group]

    To freeze/unfreeze a Service Group persistently (across reboots) :

    # hagrp -freeze -persistent[service-group]
    # hagrp -unfreeze [service-group] -persistent 
    Communication failures : Jeopardy, split brain

     




25. Question 25. Whats A Jeopardy Membership In Vcs Clusters?

    Answer :

    When a node in the cluster has only the last LLT link intact, the node forms a regular membership with other nodes with which it has more than one LLT link active and a Jeopardy membership with the node with which it has only one LLT link active.

     

26. Question 26. How To Recover From A Jeopardy Membership ?

    Answer :

    To recover from jeopardy, just fix the failed link(s) and GAB automatically detects the new link(s) and the jeopardy membership is removed from node.

     




27. Question 27. Whats A Split Brain Condition ?

    Answer :

    Split brain occurs when all the LLT links fails simultaneously. Here systems in the cluster fail to identify whether it is a system failure or an interconnect failure. Each mini-cluster thus formed thinks that it is the only cluster thats active at the moment and tries to start the service groups on the other mini-cluster which he think is down. Similar thing happens to the other mini-cluster and this may lead to a simultaneous access to the storage and can cause data corruption.

     




28. Question 28. Whats The Difference Between Multinica And Multinicb Resource Types ?

    Answer :

    MultiNICA and IPMultiNIC:

    • supports active/passive configuration.
    • Requires only 1 base IP (test IP).
    • Does not require to have all IPs in the same subnet.

    MultiNICB and IPMultiNICB:

    • supports active/active configuration.
    • Faster failover than the MultiNICA.
    • Requires IP address for each interface.
    • Troubleshooting

     

29. Question 29. How To Flush A Service Group And When Its Required ?

    Answer :

    Flushing of a service group is required when, agents for the resources in the service group seems suspended waiting for resources to be taken online/offline. Flushing a service group clears any internal wait states and stops VCS from attempting to bring resources online.

    To flush the service group SG on the cluster node, node01 :

    # hagrp -flush [SG] -sys node01

     

30. Question 30. How To Clear Resource Faults ?

    Answer :

    To clear a resource fault, we first have to fix the underlying problem.

    • For persistent resources : Do not do anything and wait for the next OfflineMonitorInterval (default – 300 seconds) for the resource to become online.
    • For non-persistent resources : Clear the fault and probe the resource on node01 :

    # hares -clear [resource_name] -sys node01
    # hares -probe [resource_name] -sys node01

     

31. Question 31. How To Clear Resources With Admin_wait State ?

    Answer :

    If the ManageFaults attribute of a service group is set to NONE, VCS does not take any automatic action when it detects a resource fault. VCS places the resource into the ADMIN_WAIT state and waits for administrative intervention.

    To clear the resource in ADMIN_WAIT state without faulting service group :

    # hares -probe [resource] -sys node01

    To clear the resource in ADMIN_WAIT state by changing the status to OFFLINE|FAULTED :

    # hagrp -clearadminwait -fault [SG] -sys node01

     

32. Question 32. How To Check The Status Of Veritas Cluster Server? Or How To Check The Status Of Vcs Cluster?

    Answer :

    hastatus –sum

     

33. Question 33. Which Is The Main Config File For Vcs And Where It Is Located? Or What Is The Main Vcs Configuration File?

    Answer :

    main.cf is the main configuration file for VCS and it is located in /etc/VRTSvcs/conf/config/.

     




34. Question 34. Which Command You Will Use To Check The Syntax Of The Main.cf? Or How To Verify The Syntax Of Main.cf Configuration File?

    Answer :

    hacf -verify /etc/VRTSvcs/conf/config

     

35. Question 35. How Will You Check The Status Of Individual Resources Of Vcs Cluster? Or How To Check The Individual Resources Status In Vcs Cluster?

    Answer :

    hares –state

     

36. Question 36. What Is Service Group In Vcs?

    Answer :

    Service group is made up of resources and their links which you normally requires to maintain the HA of application.

     




37. Question 37. What Is The Use Of Halink Command? Or What Is Halink In Veritas Cluster?

    Answer :

    halink is used to link the dependencies of the resources.

     

38. Question 38. What Is The Difference Between Switchover And Failover? Or What Is Switchover And Failover?

    Answer :

    Switchover is an manual task where as failover is automatic. You can switchover service group from online cluster node to offline cluster node in case of power outage, hardware failure, schedule shutdown and reboot. But the failover will failover the service group to the other node when VCS heartbeat link down, damaged, broken because of some disaster or system hung.

     

39. Question 39. What Is The Use Of Hagrp Command? Or How To Manage The Service Group In Vcs?

    Answer :

    hagrp is used for doing administrative actions on service groups like online, offline, switch etc.

     

40. Question 40. How To Switchover The Service Group In Vcs? Or How To Move The Service Group From One Node To Other Node In Vcs?

    Answer :

    hagrp –switch -to nodename

     




41. Question 41. How To Online The Service Groups In Vcs? Or How To Bring The Service Online In Particular Node?

    Answer :

    hagrp –online -sys nodename

     

42. Question 42. Shutdown Vcs Cluster But Keep The Services Up.

    Answer :

    hastop -all -force

     




43. Question 43. How To Check The Gab Status In Vcs Cluster? Or Confirm Vcs Has Shut Down On Each System?

    Answer :

    gabconfig -a

     

44. Question 44. How To Shutdown Gab And Confirm It's Down On Each System?

    Answer :

    • gabconfig -U
    • gabconfig -a

     

45. Question 45. How To Identify The Gab Kernel Module And Remove It From Each System In Linux?

    Answer :

    lsmod | grep gab

    rmmod gab

     

46. Question 46. How To Shutdown Llt On Each System In Vcs Cluster?

    Answer :

    lltconfig -U

     

47. Question 47. How To Identify The Llt Kernel Module And Remove It From Each System On Linux?

    Answer :

    lsmod | grep llt

    rmmod ltt

     

48. Question 48. How To Unfreeze All Service Groups?

    Answer :

    haconf -makerw

    hagrp -unfreeze <Service Group> -persistent

    haconf -dump -makero

     

49. Question 49. What Is Jeopardy In Vcs? Or What Is Jeopardy State?

    Answer :

    The state in which a node is missing one of the two required heartbeat connections. When a node is running with one heartbeat only (in jeopardy), VCS does not restart the applications on a new node. This action of disabling failover is a safety mechanism that prevents data corruption.

     

50. Question 50. What Is Split Brain In Vcs? Or What Is Split Brain Syndrome In Vcs Cluster?

    Answer :

    A split brain occurs when two independent systems configured in a cluster assume they have exclusive access to resource. this scenario can be caused when all cluster heartbeat links are simultaneously lost. Each cluster node will then mark the other cluster node as FAULTED. , usually resulting in data corruption.

     

51. Question 51. What Is The Cluster Log File For Vcs Cluster?

    Answer :

    /var/VRTSvcs/log/engine_A.log14

     

52. Question 52. Which Daemons Are Required For Ldap Server?

    Answer :

    slapd and slurpd