What Data Does Eventhouse OneLake Availability Copy?

DP-700 By islever Editorial Last updated

Ingest and transform streaming data

Short answer

E Enabling OneLake availability for the eventhouse copies only new data ingested after enablement unless the Apply to existing tables backfill option is explicitly selected.

Question

You have a Fabric workspace that contains a Real-Time Intelligence solution and an eventhouse.
Users report that from OneLake file explorer, they cannot see the data from the eventhouse.
You enable OneLake availability for the eventhouse.
What will be copied to OneLake?
  1. only data added to new databases that are added to the eventhouse
  2. only the existing data in the eventhouse
  3. no data
  4. both new data and existing data in the eventhouse
  5. only new data added to the eventhouse Correct Answer

Key Takeaways

The question tests the default copy scope of Eventhouse OneLake availability, and the trap is assuming that enabling it automatically backfills existing eventhouse data.

Eventhouse OneLake availability exposes eventhouse data in OneLake so users can access it through OneLake file explorer. This page explains that the feature copies only newly ingested data by default unless existing-table backfill is explicitly selected.

Common mistake: The most common wrong answer is D, because candidates see that the UI offers Apply to existing tables for historic backfill and assume that option is always included when OneLake availability is enabled.

Expert Analysis

Why the Answer Is Correct

Enabling OneLake availability on an eventhouse makes eventhouse data available in OneLake for OneLake file explorer, but the default copy scope is forward-looking: newly ingested data is written to OneLake after the setting is turned on. Existing tables remain in eventhouse storage unless the administrator explicitly selects the Apply to existing tables option to perform a historic backfill. Because the stem only says you enable OneLake availability and does not mention that backfill choice, the data copied is only new data added to the eventhouse. This matches Microsoft's documented behavior that existing tables aren't affected by merely enabling the feature.

Why the Other Options Are Wrong

A is wrong because OneLake availability is not limited to new databases added later; it applies to the eventhouse or database scope you enable and its new data. B is wrong because enabling the feature does not copy only existing data; without backfill it copies new data, not historic data. C is wrong because enabling OneLake availability does cause data to flow to OneLake—new records are copied. D is the tempting choice because the UI and docs mention Apply to existing tables, but that checkbox is an extra action for backfill and is not stated in the question.

Community Comment Notes

The comments split along documentation versions: Tuki93 and IshtarSQL read the stem literally and note that "Existing tables aren't affected" and only new data is synced. Several other learners, including Bin_Hashim and CMDev, vote D because current docs describe the Apply to existing tables backfill option. The key distinction is that backfill must be explicitly selected; merely enabling OneLake availability does not make existing eventhouse data appear in OneLake. The question's wording therefore supports E, even though the documented option can produce D when used.

Official Reference

https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-house-onelake-availability#how-it-works

This link opens the official vendor documentation in a new tab.

Exam Strategy

Read for an explicit backfill instruction: if the stem only says you enable OneLake availability, do not assume existing tables are included. The Apply to existing tables checkbox is an extra action for historic backfill, so choose the new-data-only option unless the question states that backfill was selected.

Frequently Asked Questions

Does enabling OneLake availability backfill existing eventhouse tables automatically?

No. Existing tables are copied only if you select the Apply to existing tables option for historic backfill; otherwise only new data is copied.

Why do some community answers choose D instead of E?

Because current docs mention an Apply to existing tables backfill option, but the stem never says that option was selected, so default behavior remains new data only.

More DP-700 FAQ →

Discussion 54 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 30 of 54

  1. Tuki93 👍 28 Answered E
    - Existing tables aren't affected. New tables are made available in OneLake. https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-house-onelake-availability#how-it-works
  2. IshtarSQL 👍 10 Answered E
    When you enable OneLake availability for an eventhouse in Microsoft Fabric, only new data ingested into the eventhouse will be synced and made available in OneLake.
  3. exnaniantwort 👍 9
    It is still E. You can turn on OneLake availability at the database or table level. When enabled at the database level, all new tables and their data are made available in OneLake. When turning on the feature, <<<you can also choose to apply this option to existing tables by selecting the Apply to existing tables option, to include historic backfill>>>. Turning on at the table level makes only that table and its data available in OneLake Only if the question mentions explicitly together the "Apply to existing tables option", otherwise, only "enable OneLake availability" does not do the backfill.
  4. Bin_Hashim 👍 7 Answered D
    Microsoft’s current docs say when you turn on OneLake availability for an eventhouse (KQL database), you can apply it to existing tables to include historic backfill, and once enabled it continues to sync new data as it arrives. So users will see both the historical data and ongoing new data in OneLake. Microsoft Learn “When enabled at the database level… you can also choose to apply this option to existing tables, to include historic backfill.” Microsoft Learn “When you turn availability back on, all data is made available in OneLake, including historic backfill.” Microsoft Learn Note: Earlier guidance (pre-2025) often said “only new data” with no backfill. The behavior has since changed/been clarified in the official docs.
  5. Sr18 👍 7
    As per documentation, now you have option to select historical backfill. So I think question's verbiage is incomplete now. Answer D : Seems more right answer now, because you have this option and may be it was selected while making the One Lake Availability.
Show 25 more comments
  1. ShazzyHawk 👍 6 Answered D
    Earlier behavior (Preview phase, mid-2024) When OneLake availability for Eventhouse was first introduced, only new data ingested after enabling the feature was written to OneLake. Existing data remained in Kusto storage unless re-ingested or exported manually. That’s why older documentation (and many early exam questions) listed E. only new data added to the eventhouse as the correct answer. Current behavior (GA – 2025 update) Per the Microsoft Fabric Real-Time Intelligence documentation, when you enable OneLake availability on an Eventhouse now: “When OneLake availability is turned on, existing data in the Eventhouse and any new data ingested afterward is made available in OneLake in Delta format.” So now: Existing data is copied and made visible in OneLake. New data continues to sync automatically going forward.
  2. CMDev 👍 5 Answered D
    The correct answer is: D. both new data and existing data in the eventhouse When you enable OneLake availability for an eventhouse, you have the option to apply this setting to existing tables by selecting the "Apply to existing tables" option. This means that both new data and existing data will be available in OneLake. As stated in the article: "When turning on the feature, you can also choose to apply this option to existing tables by selecting the Apply to existing tables option, to include historic backfill." This explains why both new and existing data will be copied to OneLake. Check this link: https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-house-onelake-availability#how-it-works
  3. QAZdbarhate12345678 👍 5 Answered D
    The correct answer is: D. both new data and existing data in the eventhouse When you enable OneLake availability for the eventhouse, both the existing data and any new data added to the eventhouse will be copied to OneLake. This allows users to access the eventhouse data from OneLake file explorer.
  4. CamiU 👍 4 Answered D
    You can turn on OneLake availability at the database or table level. When enabled at the database level, all new tables and their data are made available in OneLake. When turning on the feature, you can also choose to apply this option to existing tables by selecting the Apply to existing tables option, to include historic backfill. Turning on at the table level makes only that table and its data available in
  5. Kiket2ride 👍 4 Answered D
    I think it used to be that only new data was available but documentation now says otherwise: https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-house-onelake-availability#how-it-works When you turn availability back on, all data is made available in OneLake, including historic backfill. I vote for D then
  6. henryphchan 👍 4 Answered E
    Only new data will be loaded to OneLake
  7. VenkataPhaniPavanKumar 👍 3 Answered D
    Best thing to check the answers is to use Microsoft Copilot Copilot says When you enable OneLake availability for an eventhouse in Microsoft Fabric, the platform copies both existing and newly ingested data into the OneLake-backed file storage. This ensures that users can access all relevant telemetry data—past and present—through tools like the OneLake file explorer or other storage-compatible interfaces. This is particularly helpful when enabling lake-centric analytics or blending real-time and historical data into broader lakehouse or warehouse solutions.
  8. tall 👍 3 Answered D
    When you enable OneLake availability for an eventhouse, both new and existing data in the eventhouse will be copied to OneLake. This feature ensures that data, whether newly ingested or already present, becomes available for access through OneLake, making it easier for users to interact with and explore the data directly from OneLake file explorer.
  9. h2o_molecule 👍 3 Answered D
    You can turn on OneLake availability at the database or table level. When enabled at the database level, all new tables and their data are made available in OneLake. When turning on the feature, you can also choose to apply this option to existing tables by selecting the Apply to existing tables option.
  10. kaytee_05 👍 3 Answered D
    When you enable OneLake availability for an eventhouse, both the existing data withini the eventhouse and any new data subsequently added to it will be copied to OneLake. This ensures that the eventhouse data is acceble through OneLake file explorer for users who previously couldn't see it.
  11. Jay63002 👍 2 Answered D
    You can turn on OneLake availability at the database or table level. When enabled at the database level, all new tables and their data are made available in OneLake. When turning on the feature, you can also choose to apply this option to existing tables by selecting the Apply to existing tables option, to include historic backfill. Turning on at the table level makes only that table and its data available in OneLake. The Data retention policy of your KQL database is also applied to the data in OneLake. Data removed from your KQL database at the end of the retention period is also removed from OneLake. If you turn off OneLake availability, data is soft deleted from OneLake.
  12. DarkDerf 👍 2 Answered D
    The correct answer is: D. both new data and existing data in the eventhouse Explanation: When you enable OneLake availability for an eventhouse in Microsoft Fabric, all existing data within the eventhouse, along with any new data added afterward, is copied to OneLake. This ensures that users can access both past and future data through OneLake file explorer. This means that enabling OneLake availability makes the entire dataset in the eventhouse visible in OneLake, not just new data moving forward.
  13. Acrious 👍 2 Answered D
    I am going with D, as many have mentioned you can enable it to copy the existing data. The question is... is the question old and the question text just not updated OR are they truly trying to trick you... for anyone who has taken the test recently is the content updated to say you selected the option to include existing data?
  14. Psycho 👍 2 Answered D
    When you enable OneLake availability for an eventhouse, it does not physically copy data; instead, it creates a shortcut in OneLake that points to the eventhouse storage. This shortcut makes all existing data and any new data added later accessible through OneLake file explorer
  15. DarkDerf 👍 2 Answered E
    If we strictly follow the documentation's explanation that only new tables are made available in OneLake, then your choice E. only new data added to the eventhouse is the most precise answer. ✅ Final Answer: E. only new data added to the eventhouse
  16. Anushareddysri 👍 2 Answered D
    As per the Microsoft document you can enable onelake along with an option of existing tables as well. Here is the reference document. https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-house-onelake-availability
  17. learnazureportal 👍 2 Answered D
    D - enabling OneLake availability for an eventhouse copies both the existing data and continuously ingested new data to OneLake, making the full dataset accessible.
  18. e0f0ce6 👍 2 Answered E
    I think E is correct: https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-house-onelake-availability
  19. toniteo 👍 2
    agreed with answer E after reading and evaluating the article carefully.
  20. ageorgieva 👍 2 Answered D
    I did that in real time and it is everything - past and new data.
  21. soonapaana001 👍 1 Answered D
    Why D is Correct In Microsoft Fabric Real-Time Intelligence, enabling OneLake availability at the Eventhouse/database level includes historic data backfill: According to the official documentation ("Turn on OneLake availability for an eventhouse"), when turning on the feature, it allows including historic backfill so that existing tables and historical data already resident in the Eventhouse are converted and mirrored into Delta Parquet format in OneLake. Going forward, any new data streamed or ingested into the Eventhouse is continuously synchronized. Where the Confusion Came From During earlier preview releases of Microsoft Fabric Real-Time Analytics, enabling mirroring/OneLake availability on a KQL database only streamed incoming data prospectively (requiring manual re-ingestion for legacy data). Microsoft subsequently updated the behavior to support historical backfill upon enablement, making D the intended answer for the current Fabric DP-600 / DP-700 exams.
  22. CMDev 👍 1
    When you enable OneLake availability for an eventhouse, you have the option to apply this setting to existing tables, which includes the data already present in those tables. This means that both new data (data added after enabling OneLake availability) and existing data (data that was already in the eventhouse at the time of enabling OneLake availability) will be available in OneLake. As the article states: "When turning on the feature, you can also choose to apply this option to existing tables by selecting the Apply to existing tables option, to include historic backfill." This indicates that enabling OneLake availability can include the historical data, meaning the existing data, in addition to any new data added afterwards.
  23. Mustafa_Shazly 👍 1 Answered C
    turn on OneLake availability at the database or table level - database level >> new tables and their data are made available in OneLake. (existing tables need to anther opttion >> Apply to existing tables option) =So he didn't say (select Apply to existing tables option) and say that DB level and no new table >>>>>> So >> no data - A wrong because new database need to enable feature first (database level) - B Wrong (true if we make it on table level or DB level with Apply to existing tables option) - D and E Wrong because no new table (DB level need new table after enable option) In the last users need to see old data in exist table so we need to enable OneLake availability with Apply to existing tables option
  24. montoya207 👍 1 Answered E
    The correct answer is E. only new data added to the eventhouse. Here is the technical justification based on the sources: No Retroactive Syncing: When you enable OneLake integration for a KQL database or eventhouse, it does not "backfill" or copy data that already exists in the tables . New Data Only: The integration is designed to work only for new tables created after the setting is enabled or for new data ingested from that point forward . Default Storage: By default, KQL data is stored in the eventhouse engine and is not visible in OneLake unless this specific setting is toggled, and even then, it only applies to subsequent data movements
  25. mvg100 👍 1 Answered D
    This explains why both new and existing data will be copied to OneLake. Check this link: https://learn.microsoft.com/en-us/fabric/real-time-intelligence/event-house-onelake-availability#how-it-works Also chatbot says: When you enable OneLake availability for an eventhouse in Microsoft Fabric: Existing data in the eventhouse becomes immediately available in OneLake. New data added to the eventhouse is also automatically streamed and accessible via OneLake moving forward. This allows users to access both historical and real-time streaming data through OneLake interfaces, including the OneLake file explorer.

Reader comments & corrections

No reader corrections yet — spotted an error or have a note? Share it below.

Log in to comment, report an error, or add a note about this question.

A 500-million-row fact table exceeds the F32 Direct Lake guardrail, so increase the capacity to F64

S-grade

Shortcut caching supports only S3/GCS shortcuts and excludes files larger than 1 GB

S-grade

Updating warehouse tables requires at least the Contributor workspace role because Write is not shareable to a Viewer

S-grade

Run T-SQL in a KQL database only by prefixing the query with a -- comment line

S-grade

← Back to DP-700 Study Guide