HP CLX Migration Whitepaper

Important

Before migrating to HP Serviceguard Metrocluster on Linux, complete the following tasks:

1. HP recommends that you backup the most recent copy of the application data. This protects data loss in the event of

any operator error during the migration.

2. Verify the support matrix requirements for a Metrocluster. This migration procedure is applicable for all the replication

modes, and the Serviceguard and Metrocluster versions mentioned in the supported matrix.

For information about support matrix for 3PAR, see Feature Matrix at Serviceguard Disaster Recovery Products

Compatibility and Feature Matrix (Metrocluster with 3PAR Remote Copy) - Linux and HPUX

For infomation about support matrix for XP, see Feature Matrix at Serviceguard Disaster Recovery Products

Compatibility and Feature Matrix Metrocluster with Continuous Access for P9000 and XP) – Linux and HPUX

For information about support matrix for EVA, see Feature Matrix at Serviceguard Disaster Recovery Products

Compatibility and Feature Matrix (Metrocluster Continuous Access EVA) – Linux and HPUX

Preparing the CLX for Migration

Perform the following steps to gather accurate information and a successful migration process.

1. Serviceguard overiew and Cluster attributes mapping.

2. Mapping the CLX 3PAR or XP or EVA attributes to the Serviceguard Metrocluster attributes.

3. Migration procedure.

Serviceguard overview and Cluster attributes mapping

SG/LX cluster membership

An SG/LX cluster is a networked grouping of HP ProLiant (host systems known as nodes) having sufficient redundancy of

software and hardware that a single failure will not significantly disrupt service. Application services (individual Linux

processes) and their corresponding storage and network resources are deployed together using the package construct. In

the event of a single service, node, network, or other resource failure, SG/LX can automatically transfer control of the

package to another node within the cluster, allowing services to remain available with minimal interruption.

• Cluster Quorum

In the case of a failure, SG/LX cluster reforms with the surviving nodes. In SG/LX cluster, each node has 1 vote. During

cluster reformation, the nodes that can communicate with each other, regroup and attempt to reform a cluster. In SG/LX,

a cluster can be reformed only if the cluster quorum condition is achieved. The cluster quorum condition is met only when

a strict majority (that is, more than 50%) of the nodes running previously is available to form the cluster. All and any

remaining nodes that are not in the group with cluster quorum condition met will be reset. Since the quorum is dynamic

(the required quorum is always based on the previous running cluster membership and not on the static count of number

of nodes configured in the cluster), SG/LX clusters can reform even after repeated multiple cluster node failures.

• Split brain

If a failure in the SG/LX cluster results in equal halves (exactly 50%) of a previously running cluster, then this situation is

called as split brain. A robust arbitration method is used to break a tie. This robust arbitration method guarantees that

only one half will form a cluster and the other half will be forced to shut down. In SG/LX, arbitration can be implemented

by cluster lock. Either Lock LUN or Quorum Server can be configured as cluster lock. Configuring a membership arbitration

method (cluster lock) is must in the clusters that have two nodes.

• Lock LUN

Lock LUN acts as a quorum arbitration method in the SG/LX clusters. It is special area in the storage which is sharable by

all nodes in the cluster. During split brain situation, each partition races with other to obtain a lock on the Lock LUN. Once

the lock is obtained it is marked so that other partition can recognize the Lock LUN as “taken.” Serviceguard periodically

checks the status of Lock LUN device and log messages in the syslog in case of a failure. The Lock LUN is dedicated to use

as only membership arbitration method which is also called as cluster lock. HP recommends that the Lock LUN should

comprise of whole disk. The Lock LUN can be used only in the cluster which has nodes up to 4.