HP serviceguard t2808-90006 manual Advantages of physical replication in software are

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Disaster Tolerance and Recovery in a Serviceguard Cluster

Disaster Tolerant Architecture Guidelines

The logical order of data writes is not always maintained in synchronous replication. When a replication link goes down and transactions continue at the primary site, writes to the primary disk are queued in a bit-map. When the link is restored, if there has been more than one write to the primary disk, then there is no way to determine the original order of transactions until the resynchronization has completed successfully. This increases the risk of data inconsistency.

Also, because the replicated data is a write operation to a physical disk block, database corruption and human errors, such as the accidental removal of a database table, are replicated at the remote site.

NOTE

Configuring the disk so that it does not allow a subsequent disk write

 

until the current disk write is copied to the replica (synchronous

 

writes) can limit this risk as long as the link remains up.

 

Synchronous writes impact the capacity and performance of the data

 

replication technology.

 

 

Redundant disk hardware and cabling are required. This, at a minimum, doubles data storage costs, because the technology is in the disk itself and requires specialized hardware.

For architectures using dedicated cables, the distance between the sites is limited by the cable interconnect technology. Different technologies support different distances and provide different “data through” performance.

For architectures using common carriers, the costs can vary dramatically, and the connection can be less reliable, depending on the Service Level Agreement.

Advantages of physical replication in software are:

There is little or no time lag between the initial and replicated disk I/O, so data remains very current.

The solution is independent of disk technology, so you can use any supported disk technology.

Data copies are peers, so there is no issue with reconfiguring a replica to function as a primary disk after failover.

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Contents Page Legal Notices Contents Disaster Scenarios and Their Handling Managing an MD Device Contents Contents Editions and Releases Printing HistoryHP Printing Division Document Organization Intended AudiencePage Related Page Disaster Tolerance Evaluating the Need for Disaster Tolerance Evaluating the Need for Disaster Tolerance High Availability Architecture What is a Disaster Tolerant Architecture?Node 1 fails Pkg B Client ConnectionsDisaster Tolerant Architecture Extended Distance Clusters Understanding Types of Disaster Tolerant ClustersFrom both storage devices Extended Distance Cluster Two Data Center Setup Benefits of Extended Distance Cluster Cluster Extension CLX Cluster CLX for Linux Serviceguard Cluster Shows a CLX for a Linux Serviceguard cluster architectureBenefits of CLX Differences Between Extended Distance Cluster and CLX Continental Cluster New York Cluster Los Angeles ClusterData Cent er a Data Center B Continental ClusterBenefits of Continentalclusters Continental Cluster With Cascading Failover Comparison of Disaster Tolerant SolutionsAttributes Extended Distance Comparison of Disaster Tolerant Cluster SolutionsContinentalclusters Cluster HP-UX onlyUnderstanding Types of Disaster Tolerant Clusters Understanding Types of Disaster Tolerant Clusters Understanding Types of Disaster Tolerant Clusters WAN EVA Protecting Nodes through Geographic Dispersion Disaster Tolerant Architecture GuidelinesOff-line Data Replication Protecting Data through ReplicationPhysical Data Replication On-line Data ReplicationDisadvantages of physical replication in hardware are Advantages of physical replication in hardware areAdvantages of physical replication in software are Logical Data Replication Disadvantages of physical replication in software areDisadvantages of logical replication are Ideal Data Replication Using Alternative Power SourcesPower Circuit 1 node Alternative Power SourcesData Center a Node 3 Power Circuit Creating Highly Available NetworkingDisaster Tolerant Wide Area Networking Disaster Tolerant Local Area NetworkingDisaster Tolerant Cluster Limitations Managing a Disaster Tolerant Environment Manage it in-house, or hire a service?How is the cluster maintained? Additional Disaster Tolerant Solutions Information Building an Extended Distance Dwdm Types of Data Link for Storage NetworkingTwo Data Center and Quorum Service Location Architectures Two Data Center and Quorum Service Location Architectures Server Two Data Centers and Third Location with Dwdm and QuorumTwo Data Center and Quorum Service Location Architectures Rules for Separate Network and Data Links Guidelines on Dwdm Links for Network and Data Guidelines on Dwdm Links for Network and Data Guidelines on Dwdm Links for Network and Data Chapter Configuring your Environment Understanding Software RAID Installing XDC Installing the Extended Distance Cluster SoftwareSupported Operating Systems Prerequisites# rpm -Uvh xdc-A.01.00-0.rhel4.noarch.rpm Verifying the XDC InstallationInstalling the Extended Distance Cluster Software Configuring the Environment Configuring the Environment Configuring the Environment Setting the Value of the Link Down Timeout Parameter Configuring Multiple Paths to StorageCluster Reformation Time and Timeout Values Http//docs.hp.com Using Persistent Device NamesTo Create and Assemble an MD Device Creating a Multiple Disk Device# mdadm -A -R /dev/md0 /dev/hpdev/sde1 /dev/hpdev/sdf1 Chapter Linux #RAIDTAB= # MD RAID Commands To Edit the Datarep Variable Creating and Editing the Package Control ScriptsTo Create a Package Control Script Editing the raid.conf File To Edit the Xdcconfig File parameterTo Configure the RAID Monitoring Service Cases to Consider when Setting Rpotarget RPO Target Definitions Chapter Multipledevices and Componentdevices Raidmonitorinterval Configuring your Environment for Software RAID Disaster Scenario What happens when this disaster occursRecovery Process Disaster Scenarios and Their Handling Disaster Scenarios and Their Handling# mdadm --remove /dev/md0 # mdadm -add /dev/md0 Dev/hpdev/mylink-sdf P1 uses a mirror md0 Run the following command to S2 is non-current by less # cmrunpkg packagename Execute the commands that With md0 consisting of only N1, for example Becomes accessible from N2 Center Disaster Scenarios and Their Handling Managing an MD Device Cat /proc/mdstat Viewing the Status of the MD DeviceExample A-1 Stopping the MD Device /dev/md0 Stopping the MD DeviceExample A-2 Starting the MD Device /dev/md0 Starting the MD Device# udevinfo -q symlink -n sdc1 Removing and Adding an MD Mirror Component Disk# mdadm --remove /dev/md0 /dev/hpdev/sde Adding a Mirror Component DeviceIndex 104