Data migration is performed for various reasons including system replacement, cloud transition, and database upgrades. However, a single mistake can result in thousands of records being lost or corrupted, making thorough preparation essential.

This article covers 10 must-check items before starting data migration. It's a practical guide you can apply directly in your work.

1. Verify Source Data Backup

The first step of migration is a complete backup of source data. Store backups in at least two locations and complete a restoration test. Thinking "we have backups, so it's fine" is dangerous. It's not uncommon for backup files to be found corrupted.

2. Create Data Mapping Documentation

Create a document that maps tables, field names, and data types between source and target systems on a 1:1 basis. Record all cases where field names differ or data types are converted. This document becomes the standard for post-migration verification.

3. Define Data Integrity Criteria

Clearly define what constitutes "success." Establish specific verification criteria in advance such as matching record counts, no missing required fields, and matching sum values. Moving forward without criteria with "it looks about right" will compound problems later.

4. Set Up Test Environment

Don't migrate production data directly. Always run in a test environment first, verify results, then apply to production. The test environment should be configured as identically to production as possible.

5. Check Encoding and Locale

Encoding issues frequently occur when multilingual data including Korean, Chinese, or Japanese is involved. While UTF-8 is the standard, legacy systems often use EUC-KR or Shift_JIS. Accurately identify the source encoding before migration.

6. Large-Scale Data Processing Strategy

Moving millions of records at once can cause system load and timeout issues. Develop a strategy to process in batches and log success/failure for each batch.

7. Establish Rollback Plan

Always prepare a plan to revert to the original state when migration fails or problems are discovered. Predetermine the time required for rollback, necessary resources, and responsible personnel.

8. Stakeholder Communication

Pre-announce migration schedule, expected downtime, and scope of impact to related teams. Unexpected service interruptions lead to customer complaints and business losses.

9. Post-Migration Comparison Verification

After migration completion, you must compare and verify source and result data. Extracting to CSV or Excel and using comparison tools like DiffMate to check row-by-row and cell-by-cell differences helps quickly discover omissions or corruptions.

10. Set Post-Migration Monitoring Period

Even when everything appears normal immediately after migration, problems may surface over time. Set an intensive monitoring period of at least 1-2 weeks and establish a system for immediate response when anomalies occur.

Conclusion

The success of data migration depends on preparation. Checking each item on this list minimizes unexpected problems. Post-migration data comparison verification is a critical step that must always be performed.