# "The VSS Diff failed" error

## Issue <a href="#the_vss_diff_failedissue_occurred" id="the_vss_diff_failedissue_occurred"></a>

> The **"VSS Diff failed (An error occurred during the fast difference check; a slower method will be used instead)"** issue has occurred.

***

## Cause <a href="#the_vss_diff_failedissue_occurred" id="the_vss_diff_failedissue_occurred"></a>

This issue is usually caused by the shadow storage size being too small.

***

## Resolution

#### **Windows workstations 7, 8, 10, 11:**

1. Use the **command line** and run the following command to resize the shadow storage:

```bat
vssadmin resize shadowstorage /for=X: /on=X: /maxsize=320MB
```

2. `X` represents the disk letter (it is recommended to perform this operation on all accessible disks).

```bat
vssadmin resize shadowstorage /for=X: /on=X: /maxsize=30%
```

3. After making the changes, run the backup task again. If it still fails, contact our technical support by [submitting a request](https://xopero.com/support-center/submit-request/).

#### Windows Server:

1. Delete all shadow copies using the following two additional **command line** commands:

```bat
diskshadow
```

```bat
delete shadows all
```

2. Run the backup again. If it still fails, contact our technical support by [submitting a request](https://xopero.com/support-center/submit-request/).