---
title: "How copies are checked: Fast, Thorough or Off"
url: https://storagestudio.us/wiki/how-copies-are-checked
category: "Data Parking & moving folders"
tags: ["data parking", "moving folders", "external drive"]
summary: "Before a folder move removes your original, Storage Studio checks the copy. Fast compares every file's size, date and permissions, Thorough reads every byte on both sides, and Off checks only the total size."
updated: 2026-10-01T05:33:37.000Z
---

# How copies are checked: Fast, Thorough or Off

Before a folder move removes your original, Storage Studio checks the copy. Fast compares every file's size, date and permissions, Thorough reads every byte on both sides, and Off checks only the total size.

Every folder move checks the copy before your original is removed. The **Verification level** decides how carefully. **Fast** is the default and right for almost everyone; **Thorough** is for a drive you don't fully trust; **Off** is the quickest and checks the least.

## Where to set it

In **Data Parking**, click the **gear** in the middle column to open **Data Parking settings**, then choose under **Verification level**. The setting applies to every folder move, including moves from [Storage Inspector](https://storagestudio.us/wiki/storage-inspector) and moves back.

## The three levels

| Level | What it compares | Best for |
| --- | --- | --- |
| Fast (stat compare) | Every file's size, modified date and permissions on both sides. Any file that doesn't match is then compared byte by byte. | Everyday moves |
| Thorough (content hash) | Every byte of every file, on both sides | A drive you suspect of damaging data |
| Off (trust the copier) | Only the total size of the folder | When speed matters more than checking |

**Fast** works because a correct copy has exactly the same size, date and permissions as the original. If any file's details differ, Storage Studio reads that one file on both sides and accepts it only if the contents match.

**Thorough** reads everything twice over, once from your Mac and once from the drive, so it catches damage that the drive itself doesn't report. It takes much longer on big folders.

**Off** skips the file-by-file comparison. Storage Studio still compares the total size of the copy with the original before removing anything, so a copy that came up short is caught — but a damaged file of the right size would not be.

## Merge is checked a little differently

With **Merge**, the destination is allowed to hold files that you didn't move. **Fast** ignores those extras and still compares every file you did move. **Thorough** can't compare the whole folder in that case, so for a Merge it relies on the total-size check — which makes **Fast** the more careful choice for merges.

```mermaid
%% caption: What happens after the copy, at each verification level
flowchart TD
  A[Copy finished] --> B{Verification level}
  B -->|Fast| C[Compare size, date and permissions of every file]
  C --> D{Any differences?}
  D -->|Yes| E[Read those files on both sides]
  D -->|No| G
  E -->|Contents match| G[Check total size]
  E -->|Contents differ| X[Stop - original kept]
  B -->|Thorough| F[Read every byte on both sides]
  F -->|Match| G
  F -->|Differ| X
  B -->|Off| G
  G -->|OK| H[Remove the original or leave shortcuts]
  G -->|Too small| X
```

*Flowchart — What happens after the copy, at each verification level. Outline:*

- Copy finished
  - leads to Verification level
- Verification level
  - Fast: leads to Compare size, date and permissions of every file
  - Thorough: leads to Read every byte on both sides
  - Off: leads to Check total size
- Compare size, date and permissions of every file
  - leads to Any differences?
- Any differences?
  - Yes: leads to Read those files on both sides
  - No: leads to Check total size
- Read those files on both sides
  - Contents match: leads to Check total size
  - Contents differ: leads to Stop - original kept
- Check total size
  - OK: leads to Remove the original or leave shortcuts
  - Too small: leads to Stop - original kept
- Read every byte on both sides
  - Match: leads to Check total size
  - Differ: leads to Stop - original kept

## If a check fails

The move stops and your original stays exactly where it was. The Moves list says, in plain English, that the copy didn't match the original closely enough to be sure it was complete. Try again; if it keeps happening, something may be changing the folder while it's copied — see [When an app is holding a folder open](https://storagestudio.us/wiki/when-an-app-holds-a-folder-open) — or the drive may need attention, see [Checking your drive's health and setup](https://storagestudio.us/wiki/checking-your-drive).

While a check runs, the Moves list shows progress such as **Checking every file arrived intact — reading the copy on your drive**.

## Parallel transfers

The same settings popover has **Parallel transfers**: how many copies run at once, from 1 to 16, default 5. A lower number suits a slower drive. Changing it doesn't interrupt copies already running; the next one picks it up.

See also: [Moving folders safely](https://storagestudio.us/wiki/moving-folders-safely), [Verified copy](https://storagestudio.us/wiki/glossary-verified-copy), [What a move keeps](https://storagestudio.us/wiki/what-a-move-keeps).

More answers: https://storagestudio.us/faq

## What links here

- [A folder move failed or was cancelled](https://storagestudio.us/wiki/a-move-failed)
- [A tour of the Data Parking window](https://storagestudio.us/wiki/the-data-parking-window)
- [How Storage Studio keeps every change reversible](https://storagestudio.us/wiki/how-storage-studio-keeps-you-safe)
- [Moving folders safely](https://storagestudio.us/wiki/moving-folders-safely)
- [The drive was unplugged during a move](https://storagestudio.us/wiki/drive-unplugged-during-a-move)
- [Verified copy](https://storagestudio.us/wiki/glossary-verified-copy)
- [What a move keeps](https://storagestudio.us/wiki/what-a-move-keeps)
- [When an app is holding a folder open](https://storagestudio.us/wiki/when-an-app-holds-a-folder-open)