ADF Copy Activity Performance Issue: Why Are .XLSM Files Slower Than .XLSX or CSV Files?

Question

ADF Copy Activity Performance Issue: Why Are .XLSM Files Slower Than .XLSX or CSV Files?

Yernaidu Siraparapu 125

Hi Community,

We are experiencing a performance issue in Azure Data Factory Copy Activity when reading Excel files.

We noticed that copying data from .xlsm (macro-enabled Excel) files takes significantly longer compared to .xlsx or .csv files, even when the data volume is similar.

Has anyone encountered this behaviour? We would like to understand:

Why does ADF take more time to process .xlsm files?

Does ADF parse VBA macros, workbook metadata, or other Excel objects during the copy operation?

Are there any known limitations or performance considerations for .xlsm files?

What are the recommended best practices to improve copy performance when the source is an .xlsm file?

Ganesh Chelluri 190 Reputation points Microsoft External Staff Moderator

2026-08-04T10:10:52.0433333+00:00
Hi @Yernaidu Siraparapu ,

ADF doesn't run or parse VBA. The slowness isn't about macros, it's about the Excel read path in Copy Activity the workbook gets loaded into memory before the sheet and range are read, so it's parser-bound. Extra DIUs or parallel copies won't help.

Also worth knowing: ADF's Excel format officially covers .xls and .xlsx. .xlsm isn't listed, so even when it works there's no supported behaviour to fall back on.

What actually helps:

Convert upstream to .xlsx (macros stripped), or better, CSV or Parquet

Point the dataset at only the sheet and cell range you need

Split large workbooks into smaller files

For big files, use Mapping Data Flow instead of Copy Activity

If native .xlsm ingestion is a hard requirement for you, that's a product feature request rather than something tuning will solve.
Ganesh Chelluri 190 Reputation points Microsoft External Staff Moderator

2026-08-06T02:41:45.9466667+00:00

Hi @Yernaidu Siraparapu ,

Just checking in to see if the information provided earlier was helpful. Please let us know if you need any additional details or assistance, and we’ll gladly continue supporting you.

2 answers

Your answer

Ganesh Chelluri 190 Reputation points Microsoft External Staff Moderator

2026-08-04T10:10:52.0433333+00:00

Hi @Yernaidu Siraparapu ,

ADF doesn't run or parse VBA. The slowness isn't about macros, it's about the Excel read path in Copy Activity the workbook gets loaded into memory before the sheet and range are read, so it's parser-bound. Extra DIUs or parallel copies won't help.

Also worth knowing: ADF's Excel format officially covers .xls and .xlsx. .xlsm isn't listed, so even when it works there's no supported behaviour to fall back on.

What actually helps:

Convert upstream to .xlsx (macros stripped), or better, CSV or Parquet

Point the dataset at only the sheet and cell range you need

Split large workbooks into smaller files

For big files, use Mapping Data Flow instead of Copy Activity

If native .xlsm ingestion is a hard requirement for you, that's a product feature request rather than something tuning will solve.
Ganesh Chelluri 190 Reputation points Microsoft External Staff Moderator

2026-08-06T02:41:45.9466667+00:00

Hi @Yernaidu Siraparapu ,

Just checking in to see if the information provided earlier was helpful. Please let us know if you need any additional details or assistance, and we’ll gladly continue supporting you.

Answer 1

Senthil kumar 1,895

Hi @Yernaidu Siraparapu

.xlsx->Fast->Pure XML, no macros

.csv->Very fast->Streamable text

.xlsm->Slow->Contains VBA, binary OLE, macro streams

Thanks.

0 comments

Answer 2

You're seeing slower runs for similarly sized .xlsm files than .xlsx or CSV. ADF's Excel format officially supports only .xls and .xlsx, not .xlsm. A successful .xlsm read therefore has no supported performance contract, and Microsoft does not document Copy Activity as executing or parsing VBA projects.

Excel Copy Activity loads the workbook into memory before locating the configured worksheet and cells; CSV is simpler to parse. More DIUs or parallel copies may not improve a parser-bound run.

Convert .xlsm upstream to .xlsx with macros removed, or preferably CSV or Parquet. Configure only the required worksheet and cell range, split large workbooks, and compare execution details from representative runs. For files over 100 MB, use Mapping Data Flow, which supports streaming Excel reads, or convert before Copy Activity. If native .xlsm ingestion is mandatory, open Microsoft Support or submit a product request; it is not a documented ADF Excel capability.

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