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Archetype Attributes
As previously mentioned, archetypes are augmented or modified by the use of attributes.
The functional areas that the attributes address are:
- Security
- Persistence of data
- Reliability
- Availability
- Serviceability
- Simplicity over complexity
- Capacity
- Monitoring and measurement
- Process, procedure, change management, training, documentation, etc.
- Backup
- Recovery
- Commonality over diversity
These attributes will affect the archetypes, the exact manner in which the attributes affect or modify the archetypes is dependant on the archetype. For example, the monitoring and measurement attribute of the Data Store archetype is used for monitoring storage utilization and data access times. However, monitoring and measurement of the Physical Plant archetype is used for monitoring the datacenter environmentals such as ambient temperature, humidity, quality of power, etc.
It is important to note that reliability, availability, and serviceability are three separate attributes. While these attributes are typically considered one concept, they are three distinct attributes that may often be in contention with each other. For example, increasing the availability of an archetype may have a detrimental effect on the serviceability of the same archetype.
Consider the case of mirroring several disks with a Sun StorEdge™ D1000 array enclosure. The Sun StorEdge D1000 array enclosure has redundant power supplies, multiple SCSI controllers, and the bus can be split into two electrically distinct buses. However, the Sun StorEdge D1000 array enclosure has a common backplane for both buses. This backplane is not an availability issue or single-point-of-failure (SPOF), as its failure will not affect both halves. However, as the entire Sun StorEdge D1000 enclosure must be powered down to replace this backplane, it does provide a serviceability issue.
This is not a flaw in the Sun StorEdge D1000 array enclosure; it is a design point that must be considered. Only the needs of your application can determine if the Sun StorEdge D1000 array enclosure is sufficient.
NOTE
these attributes can be used to help enforce best practices and consistency across the archetypes. For example, if government requirements necessitate that data be retained for 10 years, the backup and recovery attributes can implement the requirement with the Data Store and Life Cycle archetypes of the pertinent systems.
More importantly, the archetype attributes are a way to document and analyze the trade-offs made when designing a system. Consider the case of a business need that dictates the creation a "one off" system to resolve a specific problem or meet a goal. For example, the site standard may be to use Sun Cluster 3.0 software to provide highly available NFS service for user's home directories and development workshops. However, business needs dictate the use of an old version of the source code sharing and management software for maintenance of a certain software project. This requirement, in turn, forces the use of Sun Cluster 2.2 software instead of the Sun Cluster 3.0 software.
This divergence from site standards is a trade-off that is made to meet the business need for maintenance of the software project. The commonality attribute of the affected archetypes can be used to document the reasons for this trade-off, as well as the impact of the trade-off on other archetypes or systems.
Note that some attributes may be detailed requirements, such as reliability, availability, or backup. Other attributes, such as simplicity and commonality, are more of a reminder to the architect, and are to be used to document any divergence from site standards.