Clustering is one of those computing concepts that is - simply great. Also
in my 'simply great' category are: client server, DHCP, and VPN. These are
technologies that just make sense and should be implemented where ever possible.
The twin benefits of clustering are load balancing and fault tolerance. One day
soon SAN (Storage
Area Network) and wireless networks will join clustering in that 'simply great'
There are at least two distinct clustering strategies: Stateful and Stateless.
Stateful is proper fault tolerance clustering, whereas Stateless is just load
balancing. The key points to check are, what application the clustering is
designed for? Does it need special hardware?
(Network Load Balancing)
Examples: VPN, IIS or Terminal Server
This is the clustering that you configured through the Network Adapter
It supports up to 32 nodes, is Stateless and automatically balances the load
when more hosts come on line. To further administer NLB there is a little known
utility nlbmgr which you can launch from the run command.
A feature of all clustering types is that each server needs a second network
adapter (dedicated IP address) which is just used to communicate with the other
From the host point of view they connect to a cluster, so each cluster needs
a DNS name and a corresponding cluster IP address.
Which ever method of clustering you use, make sure you purchase the
Enterprise or Datacenter edition of Windows 2003. The standard edition
does not support clustering.
Examples: SQL or Exchange
This method of clustering is controlled by a service that you install through Add or Remove Programs.
Note: Cluster Service requires an account much like Exchange 5.5.
Server clusters support up to 8 nodes and are Stateful. This type of
clustering supports failover and is designed primarily for fault tolerance.
The second network card maintains a 'heartbeat' with other members of the
cluster. The virtual cluster name needs to be registered in DNS.
To administer your cluster, Start (menu) Run, CluAdmin.exe. The
concept is that one node owns the resource, and the other nodes are aware
and take over in the event of failure.
Applications such as SQL and Exchange have their own administration programs
to configure Active / Active or Active / Passive clustering. Where
possible favour Active / Passive clustering, this means that in the event of
failure all the functions are taken over by a 'hot spare' server.
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Limitations of Disk configuration on server clusters.
Remember that the disks are likely to be the area where you need specialist
cluster aware hardware. At the top of the range, the storage will be
handled by NAS and SAN systems.
Disks to be used for cluster storage must be configured as basic disks and
must be formatted as NTFS.
You cannot configure cluster storage devices as dynamic disks or spanned volumes
(volume sets) if they will be used as cluster resources. You can, however, use the DiskPart.exe
utility to extend the volume of a basic cluster disk. for more information, see
It is highly recommended that you do not enable write caching
on cluster disks.
In server clusters, the process of taking resource groups offline on one node
and bringing them online on another node. When failover occurs, all resources
within a resource group fail over in a predefined order; resources that depend
on other resources are taken offline before, and are brought back online after,
the resources on which they depend.
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