File migration performance depends on multiple factors beyond just the total data size. Understanding these factors helps set realistic expectations and optimize your migration project. This guide explains the key performance considerations when migrating files to Microsoft 365.
Overview
When planning a file migration to OneDrive for Business or SharePoint Online, the time required depends on:
- Content composition - File count, folder depth, and structure
- Microsoft API limits - Throttling policies and queue restrictions
- Source platform limits - Google, Box, or other source throttling
- Permission complexity - Number of unique permissions to migrate
Key Insight
Microsoft Import Service
Cloudiway uses Microsoft's Import Service for file migrations to Microsoft 365. This service was chosen because Microsoft has implemented strict throttling policies on CSOM APIs that make them unsuitable for large-scale migrations.
How It Works
Files are uploaded to temporary Azure blob storage, then imported into SharePoint/OneDrive asynchronously. This approach allows for higher throughput while respecting Microsoft's service limits.
Service Limitations
The Microsoft Import Service has several built-in limitations that affect migration performance:
Blob Storage Lifetime
Files uploaded to temporary blob storage have a short retention period. If too many jobs are queued simultaneously, there's a risk of data loss before processing completes. Cloudiway manages this automatically.
Processing Delays
Jobs are processed asynchronously with no guaranteed completion times. Complex operations involving many folders or permissions can take hours or longer to complete.
File Submission Limits
| Limit Type | Value | Impact |
|---|---|---|
| Microsoft recommended per job | 1,000 files | Optimal processing speed |
| Cloudiway optimized limit | 200 files | Improved reliability for complex structures |
| Simultaneous jobs per user | 10 maximum | Additional jobs wait in queue |
| Queued jobs per user | 50 maximum | Excess jobs trigger 15-minute pauses |
Complex Folder Structures
Discovery Process
Before migrating files, Cloudiway runs a discovery process to pre-create the folder structure. This prevents excessive delays during the actual migration.
Discovery Speed
- Approximately 2 folders per second processing rate
- Runs before each migration pass
- Required for delta (incremental) migrations
Example Discovery Times
1,000 folders:
~8 minutes
10,000 folders:
~1.4 hours
30,000 folders:
~4 hours
100,000 folders:
~14 hours
Performance Factors
Migration speed is influenced by content composition rather than just total size:
Folder-to-File Ratio
High folder counts relative to file counts significantly slow migration. Each folder requires individual creation operations.
Warning Thresholds
15,000+ folders
Significant migration challenges expected
300,000+ files
May fail or take weeks to complete
50,000+ unique permissions
Microsoft rejects operations exceeding this limit
Expected Throughput
Under optimal conditions with proper content composition, Cloudiway can achieve:
500 GB - 1 TB
per day throughput (varies by content)
Best Practices
To optimize migration performance:
Before Migration
- Analyze content structure - Document file counts, folder counts, and total sizes
- Clean up unnecessary content - Remove duplicate files and empty folders
- Consolidate deep folder structures - Flatten overly nested hierarchies where possible
- Identify permission complexity - Review unique permissions across folders
During Migration
- Prioritize users by complexity - Start with simpler drives to validate the process
- Monitor job queues - Don't overwhelm the system with too many concurrent users
- Use delta passes - Incremental migration for users who continue working
For Large Migrations
- Consider splitting very large drives into multiple phases
- Archive rarely-accessed content instead of migrating
- Contact Cloudiway support for guidance on complex scenarios