---
id: external-drives.what-checks-run-before-transfer-drive-starts
url: https://storagestudio.us/faq/external-drives/what-checks-run-before-transfer-drive-starts
category: "External drives"
subcategory: "Upgrading, transferring and backing up the drive"
question: "Why won't Transfer Drive or Backup Drive let me pick a drive?"
alt_questions:
  - "No Drive Available in Transfer Drive"
  - "New drive not allowed for transfer"
  - "Transfer Drive says drive too small"
  - "Why is my destination drive greyed out?"
  - "transfer drive requirements"
  - "Which drives can be a Transfer Drive destination?"
short_answer: "The destination must be an external APFS or Mac OS Extended drive with room for everything on your current drive, and not already a Storage Studio drive for this Mac. Slow drives need confirming; unsuitable ones can't start."
tags: ["transfer drive", "requirements", "troubleshooting"]
related: ["https://storagestudio.us/faq/external-drives/transfer-drive-says-already-a-storage-studio-drive", "https://storagestudio.us/faq/external-drives/how-do-i-move-everything-to-a-new-external-drive", "https://storagestudio.us/faq/external-drives/transfer-drive-vs-backup-drive"]
applies_to: "all"
last_reviewed: 2026-10-01
---

# Why won't Transfer Drive or Backup Drive let me pick a drive?

Before anything copies, the destination is checked. It must be:

- an **external** drive — your internal disk and network shares are never offered;
- formatted **APFS** or **Mac OS Extended**;
- big enough for **everything on your current drive**;
- **not already** a Storage Studio drive for this Mac.

A quick speed test runs too. A slow drive or one with cautions asks you to confirm; an internal, network or too-small drive can't be started at all. If nothing suitable is connected you'll see **No Drive Available** — plug one in and press **Refresh**.