# How does drv: work, and why did realtime history stop resolving after enabling redundancy?

**URL:** <https://forum.inductiveautomation.com/t/how-does-drv-work-and-why-did-realtime-history-stop-resolving-after-enabling-redundancy/110605>\
**Category:** Ignition\
**Tags:** perspective, ignition81\
**Created:** [September 13, 2025, 12:13pm UTC](https://forum.inductiveautomation.com/t/how-does-drv-work-and-why-did-realtime-history-stop-resolving-after-enabling-redundancy/110605 "2025-09-13T12:13:39Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![paulgrimes77](https://avatars.discourse-cdn.com/v4/letter/p/bc79bd/32.png) [@paulgrimes77](https://forum.inductiveautomation.com/u/paulgrimes77)\
**Post date:** [September 13, 2025, 12:13pm UTC](https://forum.inductiveautomation.com/t/how-does-drv-work-and-why-did-realtime-history-stop-resolving-after-enabling-redundancy/110605/1 "2025-09-13T12:13:39Z")

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Environment: Ignition 8.1, redundant pair (`mo-ign22-1` master, `mo-ign22-2` backup), history provider IgnitionHistorian, tag provider default.

Before enabling redundancy, my sparklines could query realtime tag paths and history resolved fine, e.g.:  
`[default]Water/WL15/.../PV`.

After enabling redundancy, realtime paths no longer return history for those same tags. I now have to pass explicit historian paths like:  
`histprov:IgnitionHistorian:/drv:mo-ign22-2:default:/tag:Water/WL15/.../PV`.

Core questions:

1. How is the `drv:<GatewayName>:<TagProvider>` segment intended to work in redundancy on 8.1?

2. What configuration governs whether realtime paths resolve to history versus requiring explicit `histprov:/drv:/tag:`?

3. In 8.1, is it recommended to rely on realtime paths for history (letting Ignition handle redundancy), or to always build explicit `histprov:/drv:` paths in Perspective?

4. Are there known 8.1 issues where failover/promotion causes realtime history resolution to fail while explicit `drv:` paths still work?

Thanks!