OneDrive/SharePoint concurrent-download & bandwidth limits, and recommended approach for large-scale file distribution

This is a Traditional Chinese (zh-TW) forum. However, since you've asked your question in English, please allow me to respond in English as well.

Hi @Ben, 

Thank you for posting your question in the Microsoft Q&A forum.       

Regarding that you to run a load-testing script. 

1/ Can one account serve 1,200 concurrent downloads? 

OneDrive Personal (consumer / outlook.com) 

• Microsoft does not publish concurrency, bandwidth, or download-serving limits for OneDrive Personal. 
• Therefore, there is no official basis to validate a scenario involving 1,200 simultaneous downloads from a single consumer account. 
• For a planned stress test of this scale, OneDrive Personal should not be considered a supported content-distribution platform. 

OneDrive for Business / SharePoint Online 

• Microsoft does not publish a supported "maximum concurrent download" figure. 
• SharePoint Online uses dynamic throttling mechanisms that consider request rate, bandwidth consumption, service load, and usage patterns.  
• Microsoft documentation specifically notes that: 

"Running a load-testing script on SharePoint Online and you get throttled. Load testing isn't allowed on SharePoint Online." 

As a result, Microsoft does not provide an assurance that a single account, site, or shared link can sustainably serve 1,200 concurrent downloads. 

You could refer to this article: Avoid getting throttled or blocked in SharePoint Online | Microsoft Learn 

2/ What limits apply daily download/traffic bandwidth, concurrent-request throttling, and any anti-abuse blocking of shared links? At what threshold do they trigger, and how long does a temporary block last? 

Microsoft publishes some throttling-related limits,but emphasizes that they can change and are not guarantees. 

Examples from current SharePoint Online throttling guidance: 

• Per-site anonymous download (egress) limit:  
  • 100 GB over 2 hours  
• Per-site anonymous link requests:  
  • 3,000 requests per 5 minutes  
• Per-user egress:  
  • 100 GB per hour  

Microsoft also reserves the right to change these limits and notes that experience may vary.  

For your scenario: 

• 1,200 devices × 500 MB ≈ 600 GB downloaded during a single event. 
• That volume greatly exceeds the documented 100 GB / 2-hour anonymous-download limit per site if all downloads originate from one site or one anonymous sharing source.  

3/ When throttling occurs, what response should we expect (e.g. HTTP 429 / 503 / 509), and what is the recommended client handling? 

• HTTP 429 indicates the calling application sent too many requests in a time window and exceeded a predetermined limit. 
• HTTP 503 indicates the service isn't ready to handle the request. The common cause is that the service is experiencing more temporary load spikes. 

In both cases, a Retry-After header is included in the response, indicating how long the calling application should wait before retrying or making a new request. Throttled requests count towards usage limits, so failure to honor Retry-After may result in more throttling. 

4/ For distributing files to a large audience like this, what does Microsoft recommend? Is Azure Blob Storage + Azure CDN the appropriate service? Are there other recommended options? 

I’m sorry, but I’m not an Azure specialist, so I’m unable to provide authoritative guidance on whether Azure Blob Storage, Azure CDN, or another Azure service would be the most appropriate solution for your testing scenario. 

Because your planned deployment involves a large number of concurrent downloads and significant network traffic, I recommend working directly with a Microsoft Support engineer. They can review your requirements and provide guidance based on the latest service capabilities, best practices, and any applicable limitations. 

5/ If we must use OneDrive / SharePoint, what best practices minimize throttling (e.g. spreading files across multiple accounts, batching users, mirror sources)? 

The Microsoft documentation I found explains that SharePoint Online and OneDrive use dynamic throttling mechanisms and that excessive requests may result in HTTP 429 (Too Many Requests) or HTTP 503 (Server Too Busy) responses. It also recommends honoring the Retry-After header when throttling occurs. 

However, I am unable to provide architecture or performance-design recommendations for a large-scale load-testing scenario. Since your planned test involves approximately 1,200 devices and substantial download traffic, it would be best to engage a Microsoft Support engineer who can assess the proposed design and provide guidance specific to your environment. 

 The Global Admin should create a service request with Microsoft support to get advanced technical assistance and diagnostics. For detailed instructions on how to get support, please refer to Get support - Microsoft 365 admin.     

If you’re unsure who the Global Admin is within your organization, you can find guidance on locating them here: How do I find my Microsoft 365 admin? - Microsoft Support.    

Thank you for your patience and understanding. 

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