Download Multi Site Cluster

Implementing
Multi-Site Clusters
April 14 20111
Trần Văn Huệ
Nhất Nghệ CPLS
Overview of Multi-Site Clusters
Agenda:
• What Are Multi-Site Clusters?
• What Makes Multi-Site Clusters Unique?
• Why Use a Multi-Site Cluster?
• Evaluating the Business Need for a Multi-Site Cluster
• Storage Challenges for Multi-Site Clusters
• Synchronous / Asynchronous Replication?
• Network Challenges for Multi-Site Clusters
• Choosing the Appropriate Quorum Mode in Multi-Site Clusters
• Demo: Deploying a Multi-Site Cluster
What Are Multi-Site Clusters?
A multi-site cluster is a cluster that has been extended so that
different nodes in the same cluster reside in separate
physical locations
Site A
Site B
SAN
SAN
What Makes Multi-Site Clusters Unique?
• Multiple storage arrays, which are independent in each site
• Nodes commonly access storage local to their own sites
• Storage is replicated between sites
• No “true” shared disk is visible to all nodes
Site A
Site B
Changes are
made on Site A
and replicated
to Site B
Replica
Why Use a Multi-Site Cluster?
Advantages over cold standby server in a disaster
recovery site:
Automatic failover • Reduced downtime
• Lower complexity
Reduced
administrative
overhead
• Automatic synchronization of application
and cluster changes
• Better service continuity than cold
standby servers
Reduced human
error factor
• Reduced reliance on old, potentially
error-prone procedures
Evaluating the Business Need for a Multi-Site Cluster
• Because of increased cost and complexity, multi-site
clusters aren’t for every company or application
• Evaluate the application type and importance, and consider
available alternatives
• Plan for the application and hardware architecture, and
for routine failover and failback testing
Storage Challenges for Multi-Site Clusters
Challenge
Description
Requires a
separate or
third-party data
replication
solution
• Hardware (block level) storage-based
replication
• Software (file system level) host-based
replication
• Application-based replication (such as
Exchange 2007 Cluster Continuous
Replication)
Can be either
synchronous or
asynchronous
replication
• Synchronous: No acknowledgement of data
changes made in Site A until the data is
successfully written to Site B
• Asynchronous: Data changes made in Site
A will eventually be written to the storage
in Site B
What Is Synchronous Replication?
When you use synchronous replication, the host receives a
“write complete” response from the primary storage after the
data is written successfully to both storage locations
Site A
Site B
Replication
Write
Request
Write
Complete
Data
Data
Primary
Storage
Acknowledgement
Secondary
Storage
What Is Asynchronous Replication?
When you use asynchronous replication, the host receives a
“write complete” response from the primary storage after the
data is written successfully on the primary storage
Site A
Site B
Replication
Write
Request
Write
Complete
Data
Primary
Storage
Data
Secondary
Storage
Comparing Synchronous and Asynchronous
Replication
Replication Type Description
Synchronous
• Works across shorter distances
• Results in no data loss
• Requires high-bandwidth/low-latency
connections
• Allows write latencies to impact
performance
Asynchronous
• Stretches over longer distances
• Results in potential data loss on hard
failure
• Assumes large enough bandwidth to keep
up with data
• Does not significantly impact performance
Network Challenges for Multi-Site Clusters
• Inter-node communications are time sensitive; you might
need to configure these thresholds to meet the higher
WAN latency
• DNS replication might impact client reconnect times when
failover is based on hostname
• Active Directory replication latency might effect application
data availability
• Some applications might require all of the nodes to be in the
same Active Directory site
Choosing the Appropriate Quorum Mode in
Multi-Site Clusters
Quorum Mode
Choose when:
Node and Disk
Majority
• Directed by vendor only
No Majority: Disk
Only
• Directed by vendor only
Node Majority
• Limited to two sites
Node and File Share
Majority
• Three sites are available
Using Node and File Share Majority in a
Multi-Site Cluster
• File share witness allows a 2-node cluster with no shared disk
• Single file server can serve as the witness for multiple clusters
File Share
Witness
Site C
Site A
Site B
WAN
SAN
SAN
Third-Party Replication
Mechanism
Deploying a Multi-Site Cluster
When deploying multi-site clusters:

Ensure that the business requirements are met by
the solution

Use a hardware vendor to create a full solution for
multi-site clusters

Choose the correct quorum mode to properly maintain
functionality in the event of failures

Choose the correct storage replication solution to meet
these needs
Demo
Demo:
Multi Site Cluster
Demo
PC08: DC, Quorum
IP: 192.168.1.8
Site 3
Public network: 192.168.1.0/24
Site 2
Site 1
PC10:
IP: 192.168.1.10
IP: 172.16.1.10
PC09:
IP: 192.168.1.9
IP: 172.16.1.9
Private network: 172.16.1.0/16
Datakeeper replicate