Erasing a disk destroys all data on it. Copy files elsewhere before formatting.
What you will achieve
Format external drives for Mac-only, Windows-only, or shared use without surprises.
Shared drives between Mac and Windows need exFAT or FAT32 — Mac-native APFS is invisible to Windows without add-ons. Mac-only backups want APFS with GUID. Pick scheme before copying terabytes; converting later always means backup and erase.
1) Mac-only (best performance)
Disk Utility → Erase → APFS (SSD) or Mac OS Extended (HFS+) for HDD. Encryption optional. Not readable on Windows without paid drivers.
2) Windows-only
ExFAT or NTFS (read-only on Mac without NTFS drivers). Macs can format exFAT in Disk Utility.
3) Shared Mac + Windows
exFAT — no realistic file size limits for most users; no journaling — eject safely. FAT32 — 4 GB file limit — avoid for video.
4) Erase steps on Mac
- Backup data elsewhere.
- Disk Utility → select physical disk (not just volume) → Erase.
- Scheme: GUID Partition Map for Intel and Apple Silicon.
- Name, choose format, Erase.
5) Large files and permissions
exFAT has no Unix permissions — avoid for Time Machine. Use dedicated APFS partition for Mac backups and exFAT partition for swap if one disk must do both — two partitions in Disk Utility.
6) Partition schemes
GPT (GUID) required for Intel and Apple Silicon macOS boot. MBR Master Boot Record only for older Windows or legacy TVs — wrong scheme makes macOS installer refuse disk.
7) Cluster size on exFAT
Default cluster fine for mixed media. Thousands of tiny files on exFAT waste space — use APFS partition for Mac scratch and exFAT for interchange only.
8) Verify cross-platform
After format, copy 6 GB test file both directions; safely eject on Mac before plugging Windows to avoid filesystem dirty flag.
Verify
Disk mounts on intended OS; copy test file >4 GB on exFAT; safe eject works both sides.
Additional troubleshooting notes
If steps above do not resolve the issue on the first attempt, reboot once, confirm System Settings → General → Software Update is current, and retry with a second administrator account to rule out profile or keychain corruption in your daily user. Document exact error text from Console.app with timestamp — vague “it still fails” without logs wastes support time. On Apple Silicon, re-test after full shutdown (not just restart) because firmware and Thunderbolt controllers reset only on cold boot. Intel Macs should repeat test in Safe Mode to bypass third-party login items. Before erase or keychain reset, verify Time Machine or clone backup completed — batch 3 guides assume Monterey/Ventura/Sonoma/Sequoia paths in System Settings; search Spotlight for renamed panes if your macOS version labels differ slightly.