ISA Duo deployment scenarios

More info on ISA Duo

Scenario 1: one server vs. two servers

Traditionally, server services are provided by a single machine. To increase service performance, faster processors are installed and larger cache and storage space are integrated into the system. To increase fault tolerance, a backup system, which mirrors the exact configuration and services of the server system is set. When there is a system crash of the server, the backup system will be activated to carry on the server service.

• To increase server service performance

  With this one machine server system, at any time when there is a large amount of incoming requests for service, the service speed can slow dramatically. If the service request before yours is a file copy of file size 1GB. What can you do other than wait ?

  XLink's ISA Duo software widens your road to two lanes. While allows you to define a secondary server system which mirrors the complete functionality of the primary server system, ISA Duo server system makes no change in the way the server is accessed.

  The difference of this secondary server machine and traditional backup system lies in that ISA Duo's secondary server machine is actively involved in server service functioning at all time (unless you purposely define it to taking no share of service request). With this twin setting of server system, the server process speed increase is easily noticeable.

  How much incoming requests the secondary server system can take is completely up to you. An even 50% for each server is the obvious fair divide, but the flexibility of ISA Duo server system allows you to off load the complete incoming service request to one of the machines while upgrade or doing maintenance on the other machine.

• To increase fault tolerance

  When you have only one machine designated to be the server, your risk to service-down is 50%: the server is either working or not working. It is like putting all the eggs in one basket: you hope the basket won't flip.

  Using XLink's ISA Duo software, you can create a dual server system. By designating two machines for the same service, if each machine comes with its own risk to service-down of 50%, your risk of a complete service-down is now: 25% + 25% = 50%.

  What is different of the second 50% risk from the first one? The difference is: the chance of both machines failing at the same time is minimal. So, for a one machine server system, the service is down when the system crashes. Even with a backup system, it will still take some time to get the service up again. On the other hand, for XLink's ISA Duo server system, when one of the server machines dies, all service requests will be automatically shifted to the still-alive server, so a continuity of service is guaranteed.

Scenario 2: Commonly Used Clustering vs. XLink's ISA Duo server system

Today's commonly used cluster system includes three major structures. They are: shared disks, mirrored disks and shared nothing.

• Shared disks is the oldest way of server clustering. In the structure, every server can access all the other servers. It provides high level of availability and manageability.
• Mirrored disks allows each server to work co-dependently. During the process, every action on one server 'mirrors' a copy on to at least one other server. This structure works great for disaster recovery.
• Shared nothing combines the good features of the previous structures to provide high level of availbility, improved fault tolerance and scalability with easy to manage software.

Besides specialized software for service distributions, commonly used clustering structures most often require function specific hardware such as RAID Array controller, shared I/O or SCSI bus with multiple initiators, plus expensive cabling and switches.

XLink's ISA Duo server system adapts the Shared-nothing clustering structure with a fixed number of two servers in each cluster. Specifically designed for small businesses, XLink's ISA Duo server system is managed by an easy to use software installed on any regular server systems. With two systems taking up the job of one, increase of service availability is noticeable. The dual system also improves fault tolerance.

XLink's ISA Duo server system is designed specifically for server services. This includes web server, ftp server, mail server, intranet server and all other server services. The software package also includes a firewall that helps to protect the servers locally.