File name max number of characters to upload to a Lakehouse folder

[ToddChitt]

I uploaded a file to a Lakehouse folder that was 63 characters long, including the ".xlsx" extension:

"Q1_2025 <...> Jan-Mar25.xlsx"

What Fabric named the file upon upoad was:

"Q1_202~2.XLS"

It ripped out about 50 characters from the middle of the file namen, AND changed the file extension.

It this expected behavior?

Is it a BUG?

Either way, it is EXTREMELY frustrating.

After upload I could RENAME the file back to its original just fine, but that would then mess up the Data Activator Trigger that is looking for new files in the folder of type ".xlsx".

[v-sshirivolu]

Hi @ToddChitt  ,

I wanted to check if you had the opportunity to review the information provided by @jaineshp  . Please feel free to contact us if you have any further questions.

Thank you and continue using Microsoft Fabric Community Forum.

[justinjbird]

For what it's worth I attempted to upload 3 xlsx files. Different filenmame lengths - 30, 60, 70. All uploaded fine and filename intact...

[jaineshp · Accepted solution]

Hey @ToddChitt,

This looks like a known issue with Microsoft Fabric Lakehouse file uploads. Here's what's happening and how to deal with it:

What's causing this:

• Fabric is converting your filename to the old DOS 8.3 format (8 characters + 3 extension)
• This is likely due to underlying file system limitations or legacy compatibility issues
• The .xlsx to .XLS conversion suggests it's also applying old file format assumptions

Quick Solutions:

1. Pre-rename strategy: Keep filenames under 8 characters before the extension when uploading, then rename after if needed
2. Use programmatic upload: Instead of manual upload, use a notebook or pipeline to copy files - this often preserves original names:
   
   # Upload via notebook code instead
3. Data Activator workaround:
   • Set your trigger to watch for both .xlsx AND .XLS extensions
   • Or use a wildcard pattern if supported
   • Consider using file content detection rather than extension-based triggers
4. Batch rename script: Create a simple script to automatically rename files back to their original format after upload

Report it: This definitely seems like a bug worth reporting through the Fabric community or support channels. The behavior is inconsistent with modern file handling expectations.

Immediate fix: For now, either keep shorter filenames during upload or adjust your Data Activator trigger to handle both extensions until Microsoft addresses this issue.

Fixed? ✓ Mark it • Share it • Help others!

Best Regards,
Jainesh Poojara | Power BI Developer

[Koen_Verbeeck]

@jaineshp please keep AI-slop out of the community forums. If you're hellbent on using it, at least verify its output.

[ToddChitt]

Do you have a link to this issue?

I have marked your answer as a solution, but really, the solution is for Microsoft to fix the issue.

And FYI: Most of your suggestions are not procticle.

Renaming AFTER upload messes up the Trigger's FileName property.

My 'defect support system' will be to tell the client to keep their filenames shorter than about 50 characters.

So frustrating to sell something like Fabric to a client, then have to turn around and tell them that something as simple as retaining a file's name AND EXTENSION during an upload is BROKEN.

[AndyDDC]

That's a purely AI generated answer. I put your question into Copilot and it generated the exact response from that reply.

Use the advice at your own discretion.

[justinjbird]

Where is this known issue?

[AndyDDC]

The answer has been AI generated. We have no way of knowing whether the answer has any validity.