284 IBM Content Manager OnDemand Guide
12.1  Scalability, reliability, and availability defined
This section defines scalability, reliability, and availability and how they relate to a Content 
Manager OnDemand system.
Scalability
Scalability is the ability of a Content Manager OnDemand system to handle a growing amount 
of work with no performance degradation. A Content Manager OnDemand system’s 
performance improves with the addition of hardware and network resources and therefore is 
defined as a scalable system. Two types of scalability are defined:
/SM590000Horizontal scalability (or scale out): This type of scalability is achieved by adding more 
nodes, systems, or logical partitions (LPARs) to a Content Manager OnDemand instance. 
An example of horizontal scalability is adding more object servers to a Content Manager 
OnDemand instance.
/SM590000Vertical scalability (or scale up): This type of scalability is achieved by adding more 
resources to a single node in a Content Manager OnDemand instance. Typically, this type 
of scalability involves faster processors, more processors, memory, disks, or networking 
hardware.
Content Manager OnDemand is both horizontally and vertically scalable.
Reliability
Reliability is the ability of Content Manager OnDemand to perform and maintain functionality 
during regular workloads and during peak workloads. Peak workloads might occur regularly 
(for example, when everyone signs on at 9:00 a.m.) or periodically (at the end of the month 
when more processing than usual occurs). Or, peak workloads might occur sporadically (for 
example, when a special event occurs, such as a sales drive that results in more users using 
the system).
Availability
Availability is a measure of the time that a Content Manager OnDemand server or process 
functions normally, and a measure of the time that the recovery process requires after a 
component failure. It is the downtime (unavailability) that defines system availability. 
Availability is the amount of system uptime when the system is fully functional and accessible 
by all users.
Availability requires that the system provides a degree of redundancy to eliminate single 
points of failure (SPOFs). The greater the redundancy that is provided, the higher the 
availability of the system. A single physical machine is still a SPOF . For this reason, a high 
availability system topology typically involves horizontal scaling and redundancy across 
multiple machines.
High availability
High availability implies that no human intervention is needed to restore operation if a failure 
or outage occurs. A highly available system has an availability limit of at least 99%, which 
allows an average of 15 minutes each day to perform maintenance tasks (during which period 
the system is inaccessible to users). The degree of high availability that is achieved is a 
function of the amount of redundancy within the system and the degree to which this 
redundancy is automatically enabled.