---
title: Writing a custom file system provider
---

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The purpose of the CMS.IO library is to provide a way of customizing Kentico to support a file system of your choice. As described in the [Overview page](https://docs.kentico.com/k10/custom-development/working-with-physical-files-using-the-api.md), you can achieve this by developing a custom provider based on the classes contained within CMS.IO.

## Preparation

A generic file system provider project is available in the **CodeSamples** directory in your Kentico installation (e.g. _**C:\Program Files (x86)\Kentico\\\<version>\\**_). The project contains definitions of all required classes and their members for easy implementation.

1. Copy the generic project folder (**CustomFileSystemProvider**) into your web project folder.
2. Open your web project in Visual Studio.
3. Click **File -> Add -> Existing Project** and select _**CustomFileSystemProvider.csproj**_ in the **CustomFileSystemProvider** folder.
4. Add a reference to **CMS.IO** to the new custom file system provider project.
5. Add the custom file system provider project reference to the Kentico project.

## Implementation

If you choose to take advantage of the prepared provider, go through all files contained in the project and replace the **NotImplementedExceptions** inside methods with your implementation, and implement property and method overrides. You can consult the following steps for reference or if you wish to create a provider from scratch.

1. Create two separate classes that inherit from the following abstract classes:
   - CMS.IO.AbstractDirectory
   - CMS.IO.AbstractFile
2. Implement all methods defined in the abstract classes.
3. Create three other classes that inherit from the following classes:
   - CMS.IO.DirectoryInfo
   - CMS.IO.FileInfo
   - CMS.IO.FileStream
4. Override all methods and properties from those classes.
5. Create constructors for the classes listed in step 3 according to the following table:

   | Inherits from        | Constructors                                                                                                                                                                                                                                                                                                                                                          |
   | -------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
   | CMS.IO.DirectoryInfo | public DirectoryInfo(string path)                                                                                                                                                                                                                                                                                                                                     |
   | CMS.IO.FileInfo      | public FileInfo(string filename)                                                                                                                                                                                                                                                                                                                                      |
   | CMS.IO.FileStream    | public FileStream(string path, CMS.IO.FileMode mode)<br>public FileStream(string path, CMS.IO.FileMode mode, CMS.IO.FileAccess access)<br>public FileStream(string path, CMS.IO.FileMode mode, CMS.IO.FileAccess access, CMS.IO.FileShare share)<br>public FileStream(string path, CMS.IO.FileMode mode, CMS.IO.FileAccess access, CMS.IO.FileShare share, int bSize) |

## Configuration

Perform the following configuration steps to start using your custom file system provider:

1. Add the **CMSStorageProviderAssembly** key to the _appSettings_ section of your project's **web.config** file. Set the key's value to the assembly name of your custom provider.
2. Configure the project to use the provider. Choose between the following options:

   - Add the **CMSExternalStorageName** key to the _appSettings_ section of the web.config file and set the value to any identifier. This maps the project's _**entire**_ file system to the custom provider.

     – OR –
   - Use the API to create an instance of the **CMS.IO.StorageProvider** class and map specific project folders to your custom provider. See [Configuring file system providers](https://docs.kentico.com/k10/custom-development/working-with-physical-files-using-the-api/configuring-file-system-providers.md) for more information.

For example, the following web.config keys configure the application to store its _**entire**_ file system using a custom provider implemented in the "CustomFileSystemProvider" project with "custom" as the identifier:

```html

<appSettings>
...
  <add key="CMSStorageProviderAssembly" value="CustomFileSystemProvider" />
  <add key="CMSExternalStorageName" value="custom" />
...
</appSettings>

```