Availiability

Any company implementing an MES solution needs to consider a whole host of factors when deciding the level of availability required from the system.  Factors such as :

• How business critical is this system?
• If the system is unavailable ?

1. can production continue to function?
2. what is the impact of the loss of service on day to day operation?
3. if there is any data loss what will be the impact of this?
4. what is an acceptable recovery time?

• What is the likelihood that the system will be unavailable because it of system downtime versus network outage
• What is an acceptable tolerance of planned and unplanned downtime of the system?
• Who needs what information available to them, and when?
• Who will ‘own’ and maintain the infrastructure (will it be maintained by IT, or the control systems department?)
• What is the hardware budget?

There are many options available to achieve the appropriate level of availability to meet specific needs, varying from high availability servers, through virtualization to thin clients and terminal services. Customers who identify their systems as business critical, and require fault tolerant systems with an absolute minimum of downtime may decide to opt for a single, high quality, multi-purpose physical system with comprehensive internal hardware redundancy, such as Stratus servers.

Many customers are virtualizing their environments to minimise hardware costs, and maximise server utilisation.  By using software such as VMWare’s Vsphere it is possible to ‘virtualise’ hardware resources of a computer—including the CPU, RAM, hard disk and network controller—to create a fully functional virtual machine that can run its own operating system and applications just like a “real” computer. Multiple operating systems can run concurrently on a single physical computer and share hardware resources with each other.

Advantages of virtualisation include :

• Server consolidation ie multiple virtual machines on each physical machine
• Less overhead in managing the infrastructure
• Increased server utilisation
• Decreased downtime and improved reliability with business continuity and built-in data disaster recovery
• Live migration of virtual machines across servers with no disruption to users or loss of service.
• Live migration of virtual machine disks with no disruption to users or loss of service
• Dynamic load balancing of server resources
• The ability to add or remove CPU, memory, virtual storage and network devices from virtual machines as needed.