Replicate repositories using IBM ClearCase MultiSite

This article describes the replication and synchronization challenges faced in Rational ClearCase MultiSite projects and the solutions that the IBM Rational Technology Excellence Group team at Tata Consultancy Services adopted. This guide is helpful for application developers, for whom this is a common yet critical part of the software development process.

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IBM Rational Technology Excellence Group (rational.coe@tcs.com), Team of experts, Tata Consultancy Services (TCS)

The Tata Consultancy Services' IBM Rational Technology Excellence Group (TEG) is a team of experts on Rational software products and technology. The team has several breakthrough projects and several successful assignments to their credit. TEG focuses mainly on solution development and research into industry best practices, in addition to training and mentoring the project teams and consultants.



14 August 2012

Introduction

In a multisite setup, some servers act as primary servers and some as secondary. Primary servers have to be in sync for carrying out the project activities without any delay. Secondary servers need to be in sync with the primary to assist in down times. There can be various synchronization issues during the course of project. In the multisite environment, the chances of getting the replication and synchronization challenges increase.

IBM® Rational® ClearCase MultiSite® extends software configuration management across geographically distributed projects through repository replication and synchronization. It replicates and synchronizes data across the various repositories, providing users access to the current data. A Windows-UNIX setup can be used for development and configuration management in ClearCase MultiSite.

This guide for application developers describes how to deliver your work in a Rational ClearCase MultiSite environment that is running on both the Microsoft Windows and UNIX platforms. The article is based on the assumption that readers have basic knowledge of ClearCase MultiSite concepts and operations from a developer's point of view. It can serve as a reference in any project and will be helpful at both the beginner and the intermediate levels.


Types of issues in ClearCase MultiSite synchronization

For this article, we have categorized ClearCase MultiSite synchronization issues into following categories:

  • Storage issues in the source or destinations, or both
  • Packet transmission failure or packet loss
  • Failure of automated jobs
  • Replica import or export failure

In the sections that follow, we discuss these categories with reference to the issues faced and also explained the solutions that can be adopted.


Storage issues in source or destinations, or both

Sufficient amount of space should be available in the following storage locations:

  • Outgoing bay
  • Incoming bay
  • Temporary directories

Main reasons

  • Pending or failed packets stagnate in the outgoing bays and occupy the storage.
  • Packets that failed to apply to the VOBs stay in the incoming bay.
  • The temp directory is loaded with packets from the past.
  • A huge amount of data has been uploaded into the VOBs in one action. Therefore, the packets size is very large.

Analysis and possible solution

  • Error tracking from logs in /var/log under the ClearCase home directory. Send and recv are the two kinds of logs generated to distinguish between sending and receiving errors.
  • Packet clearance from the storage paths.
  • Regular maintenance of the storage paths to ensure that sufficient amount of space is present to accommodate the synchronization packets.

Packet transmission failure or packet loss

This issue is mainly due to the FTP job, which transfers the packets from the source to the destination.

Possible reasons

  • Destination is unable to receive the packets due to storage issues
  • Disruption in the transmission link
  • Server connectivity failure (Source to Destination)

Analysis and possible solution

  • Logs are available to track the job failure reasons
  • Manual transmission of the lost packets to the desired destination location
  • Manual generation of the lost packets and transmission

In addition to using FTP, you can use the in box shipping server to ship packets. The shipping server will report errors if anything is wrong, and you can use the cleartool getlog shipping command to check the shipping server log file.


Failure of automated jobs

This issue is mainly due to jobs that do not run as scheduled; therefore, replicas are left unsynchronized in a VOB family.

Possible reasons

  • Insufficient VOB or replica permissions
  • Loss of some packets (changes), thus breaking the continuity of synchronization
  • Insufficient storage in the directories mentioned in case 1
  • System failures or errors
  • Failure to connect to the destination system
  • Missing reference files

Analysis and possible solution

  • Check the VOB and replica permissions, and modify the permission suitably by using cleartool commands, such as protect and protectvob.
  • If some packets have been lost, epoch values must be reset manually to restore the continuity. This is required because epoch values will be applied sequentially to VOBs.
  • Older packets must be removed from the shipping bay storage.
  • Automated jobs can be restarted with suitable modifications in case of system failure.
  • Packets must be transferred manually to the destination systems, either by using manual FTP or through some intermediate server.
  • Some important files referenced by the jobs would have been deleted. Track the error, restore the file, and restart the automated jobs.

Replica import or export failure

Common problems encountered while attempting to import an update packet include permission and storage issues.

Possible reasons

  • Insufficient VOB or replica permissions
  • Previous synchronization packets have been lost, resulting in discontinuity in epoch values
  • Storage issues in the directories mentioned in case 1

Analysis and possible solution

  • Check the VOB/Replica Permissions and modify it suitably using cleartool commands like protect and protectvob.
  • If some packets have been lost, epoch values have to be reset manually to restore the continuity. This is required because epoch values will be applied sequentially to VOBs.
  • Older packets have to be cleared from the shipping bay storage and the temp directory.

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