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HP OpenVMS Volume Shadowing in Action

Shadowing Performance. Shadowing is primarily an availability tool, but:Shadowing can often improve performance (e.g. reads), however:Shadowing can often decrease performance (e.g. writes, and during merges and copies). Shadow Copy/Merge Performance: Why Does It Matter?. Excessive shadow-copy time

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HP OpenVMS Volume Shadowing in Action

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    1. Keith Parris Systems/Software Engineer, HP Session 1546 HP OpenVMS Volume Shadowing in Action

    2. Shadowing Performance Shadowing is primarily an availability tool, but: Shadowing can often improve performance (e.g. reads), however: Shadowing can often decrease performance (e.g. writes, and during merges and copies)

    3. Shadow Copy/Merge Performance: Why Does It Matter? Excessive shadow-copy time increases Mean Time To Repair (MTTR) after a disk failure, or a site outage in a disaster-tolerant cluster Shadow Full Merges can have a significant adverse effect on application performance Shadow copies or merges can generate a high data rate (e.g. on inter-site links for Disaster Tolerant clusters) Acceptable shadow full-copy times and link costs are often the major factors in selecting inter-site link(s) for multi-site disaster-tolerant clusters Shadow Full-Copies can also take a high amount of CPU time in interrupt state with EVAsShadow Full-Copies can also take a high amount of CPU time in interrupt state with EVAs

    4. Shadowset State Hierarchy Mini-Merge state Copy state Mini-Copy state Transient states Full Copy state Full Merge state Steady state

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