See: Installing and Configuring NAS4Free on a Windows Network. Published by Simon on October 29, 2012.
This article applies to a self-hosted ownCloud version 7.0.1 which is hosted through a Zpanel on Windows Server 2008 R2, and for which you have remote desktop admin access to the server.
Configuring the External USB and FTP.
Connect USB drive to USB port on the Server. Check Windows Explorer to see if it is present as Drive (X):\ (where “X” is the drive letter assigned by Windows, usually drive E:\). In Windows Explorer, on the USB drive, create a new folder path on the X:\ drive, such as E:\owncloud\external_storage.
Setup the FTP Account in Zpanel. Log into your Zpanel hosting account to setup an FTP account credential leading to the external USB drive path. Click on “File Management” and select “FTP Accounts.” Create a new FTP account by entering a username and password. The access type should be read and write – full access. Select the radio button to Create a new home directory. The new home directory will be the same name as the username chosen above. Click the Create button.
Access Windows Server via Remote Desktop to Adjust the FileZilla FTP Account to Point to the external USB drive file path. Since Zpanel only creates an FTP within the Directory Path configured for the Zpanel User Account, usually on “C:\zpanel\hostdata\[Zpanel_username]\External_Storage_username” drive, you need to create an alternate FTP path to the USB Drive storage path. How? Log into the Windows Server using Remote Desktop access, and click the Start button, select All Programs, then Zpanel, Management, and open the FileZilla Console. In the Filezilla console, Select the pre-configured FTP user account that you just established within Zpanel file management. How? In FileZilla console select Users and select the particular FTP user account you just established. Select Shared Folders, and you should see the original Home directory path that you pre-configured under Zpanel. For the same FTP user account, click the “Add” button and add a new directory path leading to your USB file folder path, such as E:\owncloud\external storage. Select this new path with your mouse and click the button to “Set as home directory,” in order to set this “External Storage” path as the new “Home” default folder. Make sure for “Files” that you check each checkbox to select all -> read, write, delete, append, and check each check box under Directories to select all -> create, delete, list, +Subdirectory, to ensure these authorizations are granted. You can leave the existing pre-cofigured Zpanel directory in place. For now, it is no longer the Home directory for the FTP path for this FTP user account. Click OK to exit the zpanel configuration. You can now exit the FileZilla console.
Enable External Storage in your Owncloud Admin Account. Log into your administrator account for ownCloud. Select Apps from the left menu. Select External Storage Support from the list. Under the heading External Storage Support 0.2.1, internal app, Mount external storage sources, click the Enable button.
Configure External Storage Via FTP. Remain logged in under ownCloud Administrator Account. Select “Admin” from the Menu. Within Admin, under the heading for “External Storage,” click the drop down menu on the button for “Add storage” and select “FTP.”
Change the Folder Name to your desired folder name, such as “Ext” and, under configuration, you probably need to type in localhost (for ftp server location), enter your pre-configured FTP username and your FTP password. Under “Available For” you can select ALL USERS or a particular user or particular group.
When you open your ownCloud desktop client or your web interface and login, you should see the new folder named “Ext” in your folder list. If you copy a file to that folder, it will syncronize from the server to all webdav and desktop connected devices.