Quick fix: Use robocopy in list mode (doesn’t copy, just lists differences): robocopy "C:\Source" "D:\Target" /e /l /njh /njs. Output: files that would be copied. /l = list only, /e = include subdirs, /njh /njs = no job header / summary. To compare bidirectionally: also robocopy "D:\Target" "C:\Source" /e /l /njh /njs.

robocopy’s /l flag: list files that would be processed without actually copying. Useful for comparing two directories. Shows extra files, missing files, files with different timestamps.

Symptom: Want to compare two drives using robocopy on Windows 11.
Affects: Windows 11.
Fix time: ~30 minutes (depending on drive size).

What causes this need

Compare two drives to:

Verify backup completeness.
Find missing files.
Sync directories.
Audit data integrity.
Pre-flight before merging.

Method 1: List mode for comparison

The standard route.

Open Command Prompt.
Run:
```
robocopy "C:\Source" "D:\Target" /e /l /njh /njs
```
- /e: include all subdirectories.
- /l: list only; don’t copy.
- /njh: no job header.
- /njs: no job summary.
Output: files in Source that don’t match Target (would be copied).

Reverse direction for missing in Source:

robocopy "D:\Target" "C:\Source" /e /l /njh /njs

For showing extra files in target: /xx flag.
For verbose detail: /v shows skipped files too.

This is the standard fix.

Method 2: Detailed report with /log

For documentation.

Save comparison to file:

robocopy "C:\Source" "D:\Target" /e /l /v /log:C:\compare.log

Open compare.log in Notepad / Excel.
Categories:
- Same: file in both, matching attributes.
- Newer: file in target is newer.
- Older: file in target is older.
- Lonely: file in source but not target.
- Extra: file in target but not source.
For Excel analysis: parse log columns.

For PowerShell parsing:

Get-Content C:\compare.log | Where-Object { $_ -match "Lonely|Extra" }

For comparing file count: (Get-Content C:\compare.log).Count.
For automated comparison: scheduled script that emails differences.

This is the detailed route.

Method 3: Sync after comparison

For acting on differences.

After comparison, sync source to target:
```
robocopy "C:\Source" "D:\Target" /e /copy:DAT /xo
```
- /xo: exclude older (don’t overwrite newer at target).
For mirror (delete extra from target):
```
robocopy "C:\Source" "D:\Target" /mir
```
Caution: deletes!
For bidirectional sync: not native robocopy. Use Microsoft SyncToy (legacy) or FreeFileSync (free).
For chronic backup verify: scheduled robocopy /l + email report.
For specific file types: robocopy ... *.docx /e /l.
For exclude patterns: /xf [pattern] exclude files, /xd [pattern] exclude directories.

This is the sync route.

How to verify the fix worked

robocopy output lists files differing between source and target.
Log file readable.
Comparison shows expected differences.
If sync follows: drives match.

If none of these work

If output unclear: Verbose flags: /v shows more detail. For binary content comparison: robocopy compares size + timestamp + attributes by default. For byte-level comparison: fc /b file1 file2 (Windows fc tool). For large file count: log files can be huge. Use specific filters. For network drives: slow. Wait or compare locally first. For permissions comparison: /copy:DATSO includes security. For unicode filenames: robocopy handles. For dedupe-based backups: special tools required. Borg, Restic for chunk-level comparison.

Bottom line: robocopy "C:\Source" "D:\Target" /e /l /njh /njs for comparison only. Reverse direction for files missing in source. /log: for saving report. Add /mir to sync after.