The ContinentalClusters product operates as a configuration of two MC/ServiceGuard
clusters, which can run a package on a cluster and a Recovery Cluster.
The key elements providing disaster tolerance in a continental cluster
are:
Highly available WAN networking
Data center processes and procedures coordinated
between the two cluster sites
You have a great deal of latitude in selecting these elements
for your configuration. It is recommended that you record your choices
on worksheets which can be reviewed and updated periodically.
Mutual Recovery |
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For mutual recovery, any cluster in a continental cluster
may contain both primary and recovery packages for any recovery
group. Recovery groups may be defined, for example, such that cluster
A and cluster B contain recovery packages. In this case, cmrecovercl could be run on cluster B to recover packages from cluster
A, or on cluster A to recover packages from cluster B.
Data Replication |
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Data replication between the MC/ServiceGuard clusters extends
the scope of high availability to the level of the continental cluster.
You must select a technology for data replication between the two
clusters. There are many possible choices, including:
Logical replication of databases
Logical replication of filesystems
Physical replication of data volumes via software
Physical replication of disk units via hardware
Table 5-3 “Data Replication and ContinentalClusters” is a brief discussion of how a
data replication method affects a continental cluster environment.
A detailed description of data replication can be found in Chapter
1, in the section titled "Disaster Tolerant Architecture
Guidelines." Specific guidelines for configuring the HP
SureStore E Disk Array XP Series and the EMC Symmetrix Disk Array
for physical data replication in a continental cluster are provided in
Chapters 6 and 7. White papers describing specific implementations are
also available from http://docs.hp.com/hpux/ha.
Table 5-3 Data Replication and ContinentalClusters
Replication Type | How it Works | ContinentalClusters Implication |
|---|
Logical Database Replication | Transactions from the primary application
are applied from logs to a copy of the application running on the
recovery site. (This is an example only; there are other methods.) | Requirements on CPU and I/O may limit
or prevent the Recovery Cluster from running additional applications. |
Logical Filesystem Replication | Writes to the filesystem on the primary
cluster are duplicated periodically on the recovery cluster. | CPU issues are the same as for Logical
Database Replication. The software may have to be managed as a separate MC/ServiceGuard package. |
Physical Replication of Data Volumes
via Software | Disk mirroring via LVM software. Only
limited distances are possible (up to 10 km), since mirroring is done
on disk links (SCSI or FibreChannel). | Requirements on CPU are less than for
logical replication, but there is still some CPU use. Distance limits
may make this type of replication inappropriate for ContinentalClusters. |
Physical Replication of Disk Units via Hardware | Replication of the LUNs within a disk
array through dedicated hardware links such as EMC SRDF or Continuous
Access XP. | Limited CPU requirements, but the requirement
of synchronous data replication slows replication, and may impair
application performance. Increased network speed and bandwidth can
remedy this. |
Logical data replication may require the use of packages to
handle software processes that copy data from one cluster to another
or that apply transactions from logs that are copied from one cluster
to another. Some methods of logical data replication may use a logical
replication data sender package; others may use a logical
replication data receiver package; some may use both.
Logical replication data sender and receiver packages are configured
as part of the data recovery group, as shown below under "Creating
the ContinentalClusters Configuration."
Physical Data Replication using Special Environment
files
Physical data replication generally does not require the use
of separate sender or receiver packages, but it does require specialized
logic in the package control scripts to handle the transfer of control
from the storage units of one cluster to the storage units at the
other cluster. The packages that use physical data replication with
the HP SureStore E Disk Array XP Series with Continuous Access XP
should have created a specific environment file using template /opt/cmcluster/toolkit/SGCA/xpca.env; environment file for packages that are using physical
data replication with EMC Symmetrix and the SRDF facility should
be created using /opt/cmcluster/toolkit/SGSRDF/srdf.env. Both of these templates are included with the ContinentalClusters
product.
Details on configuring the special ContinentalClusters control
scripts are in Chapters 6 and 7. Some additional notes are provided
below.
Highly Available Wide Area Networking |
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Disaster tolerant networking for ContinentalClusters is directly
tied to the data replication method. In addition to the reliability
of the redundant lines connecting the remote nodes, you also need
to consider what bandwidth you need to support the data replication
method you have chosen. A continental cluster that handles a high
number of write transactions per minute will not only require a
highly available network, but also one with a large amount of bandwidth.
Details on highly available networking can be found in Chapter 1,
in the section titled "Disaster Tolerant Architecture Guidelines." White
papers describing specific implementations are also available from http://docs.hp.com.
Data Center Processes |
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ContinentalClusters provides the cmrecovercl command that fails over all applications on the primary
cluster that are protected by ContinentalClusters. However, application failover
also requires well-defined processes for the two sites. These processes
and procedures should be written down and made available at both
sites.
Some considerations for site management are as follows:
Who notifies whom for the various
events: configuration changes, alerts, alarms?
What communication methods should be used? Email?
Phone? Beeper? Multiple methods?
Who has authority to perform what sort of configuration modifications?
Can the administrator at one site log in to the nodes on the remote
site? If so, what permissions would be set?
How often is a practice failover done?
Is there a documented test plan?
What is the process for tracking changes made to
the primary cluster?
ContinentalClusters Worksheets |
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Planning is an essential effort in creating a robust continental
cluster environment. It is recommended that you record the details
of your configuration on planning worksheets. These worksheets can
be filled in partially before configuration begins, and then completed
as you build the continental cluster. Both the site with the cluster and
the site with the Recovery Cluster should have a copy of these worksheets
to help coordinate initial configuration and subsequent changes.
Complete the worksheets in the following sections for each pair
of clusters that will be monitored by the ContinentalClusters monitor.
The following worksheet will help you describe your specific
data center configuration. Fill out the worksheet and keep it for
future reference.
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=======================================================================
Continental Cluster Name: _____________________________________________
=======================================================================
Primary Data Center Information:
Primary Cluster Name: ____________________________________________
Data Center Name and Location: ___________________________________
Main Contact: ____________________________________________________
Phone Number: ____________________________________________________
Beeper: __________________________________________________________
Email Address: ___________________________________________________
Node Names: ______________________________________________________
Monitor Package Name: __ccmonpkg__________________________________
Monitor Interval: __60 seconds____________________________________
=======================================================================
Recovery Data Center Information:
Recovery Cluster Name: ___________________________________________
Data Center Name and Location: ___________________________________
Main Contact: ____________________________________________________
Phone Number: ____________________________________________________
Beeper: __________________________________________________________
Email Address: ___________________________________________________
Node Names: ______________________________________________________
Monitor Package Name: __ccmonpkg__________________________________
Monitor Interval: __60 seconds____________________________________
|
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The following worksheet will help you organize and record
your specific recovery groups. Fill out the worksheet and keep it
for future reference.
|
=======================================================================
Continental Cluster Name: _____________________________________________
=======================================================================
Recovery Group Data:
Recovery Group Name: _____________________________________________
Primary Cluster/Package Name:_____________________________________
Data Sender Cluster/Package Name:_________________________________
Recovery Cluster/Package Name:____________________________________
Data Receiver Cluster/Package Name:_______________________________
Recovery Group Data:
Recovery Group Name: _____________________________________________
Primary Cluster/Package Name:_____________________________________
Data Sender Cluster/Package Name:_________________________________
Recovery Cluster/Package Name:____________________________________
Data Receiver Cluster/Package Name:_______________________________
Recovery Group Data:
Recovery Group Name: _____________________________________________
Primary Cluster/Package Name:_____________________________________
Data Sender Cluster/Package Name:_________________________________
Recovery Cluster/Package Name:____________________________________
Data Receiver Cluster/Package Name:_______________________________
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The following worksheet will help you organize and record
the cluster events you wish to track. Fill out a worksheet for each
primary or recovery cluster that you wish to monitor. You must monitor
each cluster containing a recovery package.
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Continental Cluster Name: _____________________________________________
=======================================================================
Cluster Event Information:
Cluster Name _____________________________________________________
Monitoring Cluster: ______________________________________________
UNREACHABLE:
Alert Interval:___________________________________________________
Alarm Interval:___________________________________________________
Notification:_____________________________________________________
Notification:_____________________________________________________
Notification:_____________________________________________________
DOWN:
Alert Interval:___________________________________________________
Notification:_____________________________________________________
Notification:_____________________________________________________
UP:
Alert Interval:___________________________________________________
Notification:_____________________________________________________
Notification:_____________________________________________________
ERROR::
Alert Interval:___________________________________________________
Notification:_____________________________________________________
Notification:_____________________________________________________
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