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High Availability Software for Windows NT
NeoCLUSTER
WHY : Demand for Availability
WHAT : Technology and Product
HOW : Configuration
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Demand for Availability
• Information is a capital asset of an
organization.
• The server systems for archiving, processing,
and conveying information must be constantly
monitored and carefully managed to provide
reliable, timely, and continuous services.
• Down time is inevitable
– Scheduled and Unscheduled
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Trends
• Distributed processing and multi-tier
client/server applications
• Multiple servers are collaborated to improve
– Load sharing
– Performance
– Availability
• Windows NT is becoming a major server
platform for mission-critical applications.
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Factors of System Availability
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CPU, memory, I/O cards
Disk
Application software
Common hardware &
system software
• Human error
24%
27%
22%
21%
6%
Source : Strategic Research Division of Find SPV
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System Availability Hierarchy
Applications
Cost
Hosts
I/O Paths
Storage Subsystem
Disk & Tape
Technology
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Ask Your Customers
• Do you use Windows NT as the platform of
your mission critical applications?
• Does system downtime mean losses to you?
• Do you need a technically and economically
affordable solution to make your NT servers
fault resilient?
• Do you need a guarding angel to watch over
your NT servers around the clock so that you
can sleep better at night?
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YES!!
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Level of System Availability
• Non-stop systems: Stratus, Tandem, Netware
SFT III
– Tightly coupled, fully duplicated configuration
– Proprietary OS
• Non-redundant systems
– Hot-plug and self-diagnostic hardware components
– Auto-retry and pro-active software
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Level of System Availability
• High Availability systems
– A cluster of loosely coupled servers
– Software based implementation
– Provide better availability/price ratio than non-stop
systems
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Cluster
• Server farm : Single Network Identity
– Database Cluster : Cluster Manager, Distributed
Lock Manager
– Computing Cluster : Parallel Computing
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Realtime Data Replication
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NeoCLUSTER
• A pure software solution for building highly
available server cluster
• Microsoft Windows NT server standard edition
version 4.0
• I386 and Alpha platforms
• Functions
– Cluster configuration and administration
– Failure detection, logging, notification, isolation,
and recovery
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Features
• Technically and economically affordable
• Fully compatible with Windows NT
• Require no software modification or
proprietary hardware
• No single point of failure
• Reliable and efficient mechanism for error
detection and fault recovery
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Features
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Intuitive and user friendly Windows GUI
Fully user configurable
Support automatic and manual switch back
Negligible impact on resource consumption
and server performance.
• Minimum human intervention
• No intrusion to routine workflow
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Operation Scenario:Hardware Perspective
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Servers
• Active Server is a pre-designated computer
responsible for providing critical services that
will be guarded by NeoCLUSTER.
• Backup Server is a pre-designated computer
that will takeover the active server under the
administration of NeoCLUSTER.
• Neither identical configured servers nor
dedicated backup server is required
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Private Network
• Dedicated interconnect for inter-server
communication.
• Three types of interconnect for redundancy
– TCP/IP : back to back or LAN connection of two
network interface cards
– RS-232 : serial cable with null modem support to
connect two COM ports
– Disk volume : two dedicate partitions on the shared
disks
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Private Network
• All instances of private net were unavailable
– A server can still rely on the public net to detect the
availability of the peer server.
– If the peer server is still available, no takeover
action will be triggered.
– If the peer server was unavailable, a takeover
action will be activate immediately.
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Public Network
• Dedicated network for clients to access servers.
• TCP/IP and NetBEUI protocols
• Each active server will carry a switchable
network ID(i.e., IP address or computer name)
– The original network IDs of both servers can
remain intact.
– Clients will connect to the switchable network ID.
– If the active server was unavailable, the backup
server will takeover the switchable network ID.
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Public Network
• NeoCLUSTER provides built-in mechanism to
identify network failure problem.
– Self-diagnostic of network availability
– Supported NICs : Intel EtherExpress PRO/100B,
3Com 3C905B, DEC 21x4x.
– Supported NIC add-on software : NIC Express
from IPMetrics(load balancing and fault-tolerance).
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Private Drives and Public Drives
• Private drives are disk volumes for storing OS
and the data that is not required to be
accessible by the backup server.
• Public drives are disk volumes on the shared
disks for storing the application software and
related data that must be accessible by the
backup server.
– Shared SCSI bus or independent host channels
– Mirroring or RAID subsystems.
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Clients
• Computer systems that access the active
servers via TCP/IP or NetBEUI protocols.
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Operation Scenario:Software Perspective
• Block diagram
Administration Tool
Cluster Monitor Service
Resource Object
Agent
Script
Cluster Service
Windows NT
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Operation Scenario:Software Perspective
• Module interaction of NeoCLUSTER
Active Server
Resource Object
Resource
Monitoring
Agent
Cluster Service
Agent
Heartbeat
Cluster
Monitor Service
Server
Heartbeat
Backup Server
Cluster Service
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Cluster Service and Cluster Monitor Service
• The core processes of NeoCLUSTER
• Two mutual-guarded NT services
– user transparent auto-restart
• Functions
– Resource objects management
– Event logging and notification
– Fault isolation and recovery
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Server Heartbeat
• Periodic messages
• Servers exchange heartbeats with each other
over the private net
• Inform the receiving server the availability of
the sending server
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Resource Object
• Components of mission critical services
– Repository of service related files : Volume
– Switchable network identity for clients to access
the services : IP Address or Computer Alias Name
– The service itself : File Share, NT Services, or User
Defined
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Resource Object
• Volume
– Disk partitions on the public drives.
– The drive letter mapping and partition information
of a volume must be identical when viewed from
both servers. This ensures that no matter which
server is the active server, the volume can be
accessed with the same drive letter.
– NeoCLUSTER provides “volume locking” to
ensure exclusive volume access.
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Resource Object
• IP Address
– A switchable network identity for TCP/IP.
• Computer Alias Name
– A switchable network identity for NetBEUI.
• File Share
– Shared directories that are accessible by clients.
– Both servers must use the same share name.
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Resource Object
• NT Services
– Most application software for Windows NT are
implemented as NT services.
• User Defined
– For configuring the application software that is not
implemented as NT services.
– For grouping related resource objects into resource
hierarchy.
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Resource Hierarchy
• Each mission critical service is formulated and
manipulated as a resource hierarchy
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Resource Hierarchy
• A resource hierarchy is an integrated entity.
• A resource hierarchy identifies the required
resource objects and the proper sequence to
activate those resource objects.
• A single resource object is a generic resource
hierarchy.
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Agents
• Windows NT executable files
• Availability monitoring and error detection
– Intelligent and light-weighted
» Least system resource consumption
» Minimum impact on system performance
– Efficient and reliable
» No critical failure will be neglected
» Real-time respond to failure to reduce downtime
» No false alarm
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Agents
• Built-in agents
– Server, public net, public drives
– Resource objects
• Agent API and template
– Custom agent development
– An open interface to communicate and interact
with other programmable third party hardware and
software management tools
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Agent Heartbeat
• Periodic messages
• Agent send heartbeats to the Cluster Service to
inform the Cluster Service the availability of
the resource object monitored by the agent
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Scripts
• Windows NT executable files
• Auto-initiated
– Start a series of programs
– Terminate a series of programs
– Monitoring a series of programs
– Trigger event notification programs
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Administration Tool
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Intuitive and user friendly
Interactive point-and-click Windows GUI
Menu-driven and form-based interface
Icon-based real-time status monitoring
Support dynamic configuration and real-time
synchronization
• Remote administration using Web browser is
freely available from third parties
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Administration Tool
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Availability Recovery
• Critical factors of failover/takeover : Volume,
NT Service, User Defined
• Mechanisms
– Failover is initiated by the active server
– Takeover is initiated by the backup server
• Failover/Takeover
– The active server deactivate corresponding
resource hierarchy
– The backup server reactivate the resource hierarchy
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Availability Recovery
• Switch back/Fail back
– Switch a resource hierarchy back to the original
active server from the backup server
» The original active server has recovered
» The backup server detects that the active server has
recovered
– Retain the original load distribution
» Asymmetric configuration : active/backup servers with
different capacity
» Symmetric configuration : two active, mutual takeover
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Clients
• Client-end applications will connect to
switchable network IDs
• No need to reconfigure or modify the clientend applications
• Reconnection after a failover operation is
application dependent
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Clients
• Stateless applications
– NFS service or UDP-based applications
– User transparent
• Stateful applications
– Client/server RDBMS applications or TCP-based
applications
– The client applications will loose their connection
to the server
– Manually reconnect to server is required
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Supported Application
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File Sharing
Printer Spooler
Internet Servers(FTP, WWW, etc.)
RDBMS(Microsoft, Oracle, Sybase, Informix)
Microsoft Exchange Server, Lotus Notes
Server
• NT Service-based application software
• TCP/IP or NetBEUI-based client/server
applications
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Future Improvements
• Multiple error notification facilities
– Server side visual and audio alarm
– Message broadcasting
– E-mail
– Pager
– SNMP agent
• Simplified GUI
• N to 1 cluster configuration
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Supported Configurations
• Active/Backup
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Supported Configuration
• Active/Active
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Supported Configuration