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[그림] 그룹 시작/종료시 의존 관계에 있는 리소스들의 온라인/오프라인 순서
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많은 응용프로그램들은 디스크(혹은 스토리지)에 데이터를 기록합니다. 따라서 응용프로그램들은 디스크에 의존하는 형태로 관계가 이루어져야 합니다.
데이터베이스의 경우는 데이터를 기록할 디스크를 지정해야 합니다. 따라서 데이터베이스는 디스크에 의존하도록 데이터베이스를 부모로 디스크를 자식으로 의존 관계를 설정합니다.
클라이언트에서 데이터베이스에 접속 할 수 있는 IP 주소가 필요하다면 네크워크주소를 자식으로 데이터베이스를 부모로 의존 관계를 설정합니다.
이 의존 관계를 바탕으로 MCCS에서는 그룹을 온라인 할 때, 네트워크주소 리소스와 디스크 un-lock 상태가 정상적으로 실행되었는지 확인한 후에 데이터베이스를 구동시킵니다.
따라서 데이터베이스는 네트워크주소 리소스, 디스크 리소스를 모두 의존하는 관계로 설정되어야 합니다.
지금까지의 관계로 의존성을 구성해보면 다음과 같은 형태가 됩니다.
[Figure] Dependency of database application
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Actions due to dependency
Online/Offline of the group is performed from bottom to top according to the dependency in case of online, and from top to bottom in case of offline.
Following are a few examples how MCCS manages the resources after dependency link among the resources when a resource is failed. Attributes and state of resources are defined as the figure below.
[Figure] Resource State Information Charts
Critical Attributes
- Failure occurs from a resource on which critical resource depend.
[Figure] Example of Failure Occur 1
- As a failure is occurred at resource r2, resource r1 will be taken offline. (Since resource r1 depends on resource r2 which is failed, resource r1 may cannot be online properly.)
- Since resource r1 has critical attribute, resource r3 and r4 will be taken offline in order to failover the group.
- As a result, resource r2 is considered as failure and all resources in the group will be taken offline
- Non-critical Resources
[Figure] Example of Failure Occur 2
- Resource r1 which is not critical is online status.
- When resource r2 get failed, resource r1 will be taken offline because it dependent on resource r2.
- As r1 resource is not critical, group failover will be not performed. Therefore, the group will be partial online status.
RestartLimit Attribute
RestartLimit is an attribute of the resource type. This value determines how many times the recovery will be attempted until it is finally confirmed that it is failure.
(Please refer to "6. Resource Type" for more details.)
[Figure] Example of Failure Occur 3
- On the assumption that the value of RestartLimit is 1 for resource r2, the first failure has occurred.
- MCCS will bring online resource r2 again as the value of RestartLimit.
At this time, resource r1 which depends on resource r2 will be taken offline. - resource r2 restart.
- resource r1 online.
- When another failure occurs on resource r2, all of the resource will be taken offline from resource r1 to r3 by order.
- Resource r3 will be taken offline.
- As a result, resource r2 is considered as failure and all resources in the group is offline status in the node.