What causes AzureAppendBlobConcurrentWriteConflict?

Multiple pipeline runs targeting the same append blob path are executing concurrently. A ForEach loop with parallel iterations all append to the same blob file. An external process is also appending to the blob while the ADF activity runs

How do I fix AzureAppendBlobConcurrentWriteConflict?

Ensure only one copy activity writes to a given append blob path at a time — add sequential execution constraints.. Use a unique file naming pattern per run (include run ID or timestamp) to avoid shared blob paths.. Switch to block blobs if concurrent writes are needed — block blobs support the merge-files pattern more reliably.

Medium severitydata source

Power BI Refresh Error:
AzureAppendBlobConcurrentWriteConflict

What does this error mean?

Multiple ADF copy activities are writing to the same Azure Append Blob simultaneously, causing a write conflict. Append blobs do not support concurrent appends from different clients.

Common causes

1Multiple pipeline runs targeting the same append blob path are executing concurrently
2A ForEach loop with parallel iterations all append to the same blob file
3An external process is also appending to the blob while the ADF activity runs

How to fix it

1Ensure only one copy activity writes to a given append blob path at a time — add sequential execution constraints.
2Use a unique file naming pattern per run (include run ID or timestamp) to avoid shared blob paths.
3Switch to block blobs if concurrent writes are needed — block blobs support the merge-files pattern more reliably.

Frequently asked questions

Does this error affect all pipeline runs or just the current one?

Depends on the root cause. A persistent misconfiguration fails every run; a transient issue may resolve on retry. Check the run history.

Can this error appear in Azure Data Factory and Microsoft Fabric pipelines?

Yes — the same connector errors appear in both ADF and Fabric Data Factory pipelines.

How do I see the full error detail for an ADF pipeline failure?

In ADF Monitor, click the failed run, then the failed activity. The detail pane shows the error code, message, and sub-error codes.

Will downstream Power BI datasets be affected when an ADF pipeline fails?

Yes — a dataset refreshing after the pipeline will use stale data or fail if the target table was cleared. The Power BI refresh may succeed while serving wrong data.

Official documentation: https://learn.microsoft.com/en-us/azure/data-factory/connector-troubleshoot-azure-blob-storage