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Copyright IBM Corporation 2010 Trademarks

Introduction to PowerHA Page 1 of 18

Introduction to PowerHA

Power high availability

Tejaswini Kaujalgi([email protected])

Software Engineer

IBM India Software Labs

Uma Chandolu([email protected])

Senior Staff Software EngineerIBM

17 August 2010

PowerHA for AIX is the new name for HACMP (High Availability Cluster Multiprocessing).

HACMP is an application that makes system fault resilient and reduces downtime of

applications. This article introduces PowerHA and provides a detailed explanation of how

to configure a two node cluster.Considering the demand for this configuration from various

customers, this document is very useful for understanding PowerHA and setting up a two node

cluster.

Introduction

In today's increasing business demands, critical applications need to be available all the time,

and the system needs to be fault tolerant. But these fault tolerant systems always come with a

heavy cost. Hence, there is need of an application which provides these facilities and is also cost

effective.

A high availability solution can ensure that the failure of any component of the solution does

not cause the application and its data to be unavailable to the user community. This is achieved

through the elimination, or masking, of both planned and unplanned downtime by eliminating

single points of failure. Also, there is no specialized hardware required to make an application

highly available. PowerHA does not perform some administrative tasks like backups, time

synchronization, and any application specific configuration.

Figure 1 is an illustration of the failover capacity. When one server goes down, the other takes

over.
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Figure 1. Failover capacity

Overview of PowerHA

The terms PowerHA and HACMP are used interchangeably. As mentioned earlier, it eliminates

single points of failure (SPOF). The following table shows possible SPOFs:

Cluster object Eliminated as SPOF by:

Node Use multiple nodes

Power source Using multiple circuits or uninterrupted power supplies

Network adapter Using redundant network adapters

Network Using multiple networks to connect nodes

TCP/IP subsystem Using non-IP networks to connect adjoining nodes and clients

Disk adapter Using redundant disk adapter or multi-path hardware

Disk Using multiple disks with mirroring or raid

Application Adding nodes for takeover; configuring application monitor

VIO server Implementing dual VIO server

Site Adding an additional site

The main goal is to have 2 servers so that if one fails, the other takes over. PowerHA is a

clustering technology that provides both failover protection by having redundancy and horizontal

scalability through concurrent/parallel access.

PowerHA terminology

There are various terminologies used in PowerHA. They can be classified into topology

components and resource components.

The topology components are basically the physical components. They include:


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Nodes: System p servers can be standalone partitions or vios clients

Networks: IP networks and non-IP networks

Communication interfaces: Token ring or Ethernet adapters

Communication devices: RS232 or heartbeat over disk

The resources components are the logical entities that will be made highly available. They include:

Application server: It involves the start/stop scripts of the application

Service IP address: The end users are generally given an IP address to connect to the

application. This IP address is mapped to a node where the application is actually running.

Since the IP address needs to remain highly available, it is a part of the resource group.

File system: Many applications require the file systems to mounted.

Volume group: Volume groups are required to be made highly available with many

applications.

All the resources together form an entity called a resource group. PowerHA handles this as

a single unit. It keeps the resource groups highly available. Resource groups have policies

associated with it. Those are:

1. Startup policy: This tells which node the resource group should activate

2. Fallover policy: When a failure happens, this determines the fallover target node

3. Fallback policy: This tells whether or not the resource group will fallback.

Whenever a failure happens, it looks for these policies and works accordingly.

The subsystems of PowerHA

Figure 2. Subsystems of PowerHA

The illustration above shows how PowerHA comprises of a number of software components:

The cluster manager (clstrmgr) is the core process that monitors cluster membership. The

cluster manager includes a topology manager to manage the topology components, a


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resource manager to manage resource groups, an event manager with event scripts that

works through the RMC facility, and RSCT to react to failures.

The clinfo process provides an API for communicating between cluster manager and your

application. Clinfo also provides remote monitoring capabilities and can run a script in

response to a status change in the cluster.

In PowerHA V5, clcomdES allows the cluster managers to communicate in a secure mannerwithout using rsh and the /.rhost files.

Configuration of a 2 node cluster

Before starting off with the configurations, let's look at the networking and the storage

considerations of PowerHA.

Networking

PowerHA uses networks to detect and diagnose failures, as well as providing clients with highly

available access to applications.

Internode communication also happens through networks. PowerHA detects three kinds of failures

directly. Those are the network, NIC and node failure. It detects and diagnosis through the use of

RSCT daemon. RSCT detects the loss of heartbeat packets that are sent across all the networks

and determines the exact loss (network, NIC or node failure).

Figure 2 shows that the heartbeat packets are transferred and received by all NICs, which helps in

determining the failures.

Figure 3. Cluster representing heartbeat packets

If the heartbeat packets are stopped, then both nodes assume that the other is down and each will

try to bring the resource group online. This could result in massive data corruption.

To avoid this, PowerHA uses two kinds of networks:

1. IP networks: Examples are Ethernet, Ether channel, etc.

2. Non-IP networks: An example is RS232 (this is needed to make sure that even if the network

goes down, PowerHA is capable of differentiating between network failure and node failure)


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IP address take over (IPAT)

Most applications require that the IP address be highly available. To ensure this, we include this

service IP into the resource group. The movement of this service IP from one NIC to another is

called as IP address take over. There are two ways to use IPAT:

1. IPAT via aliasing: PowerHA adds the service IP address to the NIC (accomplished using AIX

IP aliasing feature).

2. IPAT via replacement: PowerHA replaces the Interface IP address with the Service IP.

Storage

Storage can be broadly classified into two types:

1. Private storage: Owned by only one node

2. Shared storage: Owned by one or more nodes in the cluster

All applications' data resides in the shared storage. To avoid data inconsistency, shared storageprotection can be done in the following ways:

1. Reserve/release-basedshared storage protection: Used with standard volume groups

2. RSCT-basedshared storage protection: Used with enhanced concurrent volume groups

HACMP 5.x supports the RSCT-based style of shared storage protection, which relies on AIXs

RSCT component to coordinate the ownership of shared storage when using enhanced concurrent

volume groups in non-concurrent mode.

Configuration

Before starting with the configuration, the cluster must be properly planned. The online planningworksheets (OLPW) can be used for the planning purpose. Here, it explains the configuration of

a two node cluster. In the example provided, both nodes have 3 Ethernet adapters and 2 shared

disks.

Step 1: Fileset installation

After installing AIX, the first step is to install the required filesets. The RSCT and BOS filesets can

be found in the AIX base version CDs. The license for PowerHA needs to be purchased to install

the HACMP filesets. Install the following filesets:

RSCT filesets BOS filesets HACMP 5.5 filesets

rsct.compat.basic.hacmp

rsct.compat.clients.hacmp

rsct.basic.hacmp

rsct.basic.rte

rsct.opt.storagerm

rsct.crypt.des

rsct.crypt.3des

rsct.crypt.aes256

bos.data

bos.adt.libm

bos.adt.syscalls

bos.clvm.enh

bos.net.nfs.server

cluster.adt.es

cluster.es.assist

cluster.es.cspoc

cluster.es.plugins

cluster.assist.license

cluster.doc.en_US.assist

cluster.doc.en_US.es

cluster.es.worksheets

cluster.license

cluster.man.en_US.assist

cluster.man.en_US.es


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Image 2. Configuration of a private IP address

Similarly, configure en2 with private IP 10.10.210.21 and start the TCP/IP services. Next, you need

to add the IP addresses (of both node1, node2 and the service IP which db2live here) and the

labels into /etc/hosts file. It should look like the following:

# Internet Address Hostname # Comments

127.0.0.1 loopback localhost # loopback (lo0) name/address

192.168.20.72 node1.in.ibm.com node1

192.168.20.201 node2.in.ibm.com node2

10.10.35.5 node2ha1

10.10.210.11 node2ha2

10.10.35.4 node1ha110.10.210.21 node1ha2

192.168.22.39 db2live

The idea is that you should include each of the three ports for each machine with relevant labels

for name resolution.

Perform similar operations on node2. Configure en0 with the public IP and en1 and en2 with

private IPs and edit the /etc/hosts file. To test that all is well, you can issue pings to the various IP

addresses from each machine.

Step 4: Storage configuration

We need to have a shared storage to create heartbeat over FC disk. The disks need to be

allocated from SAN. Once both the nodes are able to see the same disks (this can be identified

using LUN number), heartbeat over disks will be configured.

This method does not use Ethernet to avoid a single point of failure from the Ethernet network/

switches/protocols. The first step is to identify the available major number on all the nodes (as

shown on Image 3below).


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Image 5. Logical Volume creation

Once lv is created, initialize the logform with the following:#logform /dev/hbloglv

Repeat this process to create another LV of type jfs and named hblv (but otherwise identical).

3. Next, we create a filesystem. To do that, enter the following:#smitty crfs ->Add a Journaled File System -> Add a Journaled File System on a

Previously Defined Logical Volume -> Add a Standard Journaled File System

Here enter the lv name "hblv", lv for log as " hbloglv" and the mount point /hb_fs

Image 6. Filesystem creation in a Logical Volume

Once the Filesystem is created, try mounting the file system. Before moving to node2,unmount /hb_fs and varyoffvg hbvg.

On Node 2

1. Identify the shared disk using PVID. Import the volume group with same major number (we

used 100) from the shared disk (hdisk1):#importvg -V 100 -y hbvg hdisk1

2. Varyon the volume group and disable auto start at mount.


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#varyonvg hbvg

#chvg -an hbvg

Now, you should be able to mount the filesystem. Once done, unmount the filesystem and

varyoffvg hbvg.

3. Verification of Heartbeat over FC:Open 2 different sessions of both the nodes. On node1, run following command where hdisk1

is the shared disk.#/usr/sbin/rsct/bin/dhb_read -p hdisk1 -r

On node2:/usr/sbin/rsct/bin/dhb_read -p hdisk1 -t

Basically, one node will heartbeat to the disk and the other will detect it. Both nodes should

return to the command line after the reporting link operates normally.

Application specific configuration

If you are creating any application (for example DB2 server) highly available, specific configuration

needs to be done. That is beyond the scope of this article.

HACMP related configuration

Network takeover on both nodes:

1. Run grep -i community /etc/snmpdv3.conf | grep public and ensure that there is an

uncommentedline similar to COMMUNITY public public noAuthNoPriv 0.0.0.0 0.0.0.0.2. Next we need to add all the IP addresses of nodes, NIC's in the /etc/rhosts file.

# cat /usr/es/sbin/cluster/etc/rhosts

192.168.20.72

192.168.20.201

10.10.35.5

10.10.210.11

10.10.35.4

10.10.210.21

192.168.22.39

Configuring PowerHA cluster

On Node 1:

1. First, define a cluster:#smitty hacmp --> Extended Configuration --> Extended Topology Configuration -->

Configure an HACMP Cluster --> Add/Change/Show

an HACMP Cluster


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Image 7. Defining a cluster

Press Enter; now, the cluster is defined.

2. Add nodes to the defined cluster:#smitty hacmp --> Extended Configuration --> Extended Topology

Configuration --> Configure HACMP Nodes --> Add a Node to the HACMP

Cluster

Image 8. Adding nodes to a cluster

Similarly, add another node to the cluster. Now, we have defined a cluster and added nodes toit. Next, we will make the two nodes communicate with each other.

3. To add networks, we will add two kinds of networks, IP (Ethernet) and non-IP (diskhb).#smitty hacmp --> Extended Configuration --> Extended Topology

Configuration--> Configure HACMP Networks --> Add a Network to the

HACMP Cluster

Select "ether" from the list.


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Image 9. Adding networks to the cluster

After this is added, return to "Add a network to the HACMP cluster" and also add the diskhb

network.

4. The next step establishes what physical devices from each node are connected to each

network.#smitty hacmp --> Extended Configuration --> Extended Topology

Configuration--> Configure HACMP Communication Interfaces/Devices

--> Add Communication Interfaces/Devices -->Add Pre-defined

Communication Interfaces and Devices--> Communication Interfaces

Pick the network that we added in the last step (IP_network) and enter configuration similar to

this:

Image 10. Adding communication devices to the cluster

There should be a warning about an insufficient number of communication ports on particular

networks. These last steps need to be repeated for the different adapters to be assigned to

the various networks for HACMP purposes. The warnings can be ignored. By the time all

adapters are assigned to networks, the warnings must be gone. In any case, repeat for all

interfaces.Note that for the disk communication (the disk heartbeat), the steps are slightly different.#smitty hacmp --> Extended Configuration --> Extended Topology

Configuration--> Configure HACMP Communication Interfaces/Devices --> Add

Communication Devices

Select shared_diskhb or the relevant name as appropriate and fill in the details as below:


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Image 13. Adding resources - Application server

This specifies the server name, the start and the stop scripts needed to start/stop the

application server. For applications such as DB2, WebSphere, SAP, Oracle, TSM, ECM,

LDAP, IBM HTTP, the start/stop scripts come with the product. For other applications,

administrators should write their own scripts to start/stop the application.

The next resource that we will add into the resource group is a service IP. It is through this IP

only that the end users will connect to the application. Hence, service IP should be kept highlyavailable.#smitty hacmp --> Extended Configuration-->Extended Resource

Configuration-->HACMP Extended Resources Configuration-->Configure HACMP

Service IP Labels/Addresses--> Add a Service IP Label/Address

Choose "Configurable on Multiple Nodes" and then "IP_network". Here we have db2live as

the service IP.

Image 14. Adding resources - Service IP

Now the resources are added, we will create a resource group (RG), define RG policies, and

add all these resources to it.#smitty hacmp --> Extended Configuration-->HACMP Extended Resource Group

Configuration--> Add a Resource Group


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Image 15. Resource group creation

Once RG is created, we can change attributes of it using,#smitty hacmp --> Extended Configuration-->HACMP Extended Resource Group

Configuration-->Change/Show Resources and Attributes for a Resource Group

Select db2_rg and configure as desired:

Image 16. Defining various attributes of the resource group

6. Verification and synchronization

Once everything is configured on the primary node (node1), we need to synchronize this with

all other nodes in the cluster. To do that, do the following:#smitty hacmp--> Extended Configuration--> Extended Verification and

Synchronization


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Image 17. Verification and synchronization of the cluster

This will check the status and configuration of the local node first, and then it will propagate

the configuration to the other nodes in the cluster, if they are reachable. There should be

plenty of details on any errors and passes, too. Once this is done, your cluster is ready. You

can test it by moving the RG manually. To do that, do the following:#smitty hacmp--> System Management (C-SPOC)--> HACMP Resource Group and

Application Management--> Move a Resource Group to Another Node / Site-->Move Resource Groups to Another Node

Choose "node2" and press Enter. You should see the stop scripts running on node1 and start

scripts running on node2. After few seconds, the RG will be online on node2.


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Resources

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About the authors

Tejaswini Kaujalgi

Tejaswini Kaujalgi works as Systems Software Engineer in the IBM AIX UPT Release

team in Bangalore. She has been working on AIX, PowerHA, Security, and VIOS

components on pSeries for more than 3 years at IBM India Software Labs. She

has also worked on various customer configurations using LDAP, Kerberos, RBAC,

PowerHA and AIX on pSeries. She is an IBM certified System p Administrator. You

can reach her at [email protected].

Uma Chandolu

Uma M. Chandolu works as a Development Support Specialist on AIX. He has five

years of extensive hands-on experience in AIX environments and demonstrated

expertise in AIX system administration and other subsystems. He has experience

interfacing with customers and handling customer-critical situations. He has been

recognized as an IBM developerWorks contributing author. He can be contacted at

[email protected].

Copyright IBM Corporation 2010

(www.ibm.com/legal/copytrade.shtml)

Trademarks

(www.ibm.com/developerworks/ibm/trademarks/)
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