Let’s get to work. Follow these steps in order. The first solution will resolve the issue for 80% of users.
The FST cache filename is often derived from the game’s title ID (e.g., RZDE01.fst for "The Legend of Zelda: Twilight Princess"). If the game’s path contains special characters, emojis, or spaces, or if the underlying iOS file system (APFS) has strict naming rules, the write operation may fail.
If none of the above work, try:
The "iOS-FS failed to write new FST" error is almost always a permission or corruption issue within the virtual Wii storage. With the steps above, you should be back to gaming in minutes.
Last updated: March 2025 – Applies to Dolphin 5.0 and newer development builds.
Dolphin maintains a virtual Wii NAND (flash memory) in a folder called Wii. If that NAND is corrupted or has an inconsistent file system, IOS-FS operations can fail. dolphin ios-fs failed to write new fst
The "dolphin ios-fs failed to write new fst" error is intimidating because of its technical jargon, but it is almost always a permissions or file-system issue, not a fatal hardware error. By methodically working through the solutions above—starting with running as administrator and moving to NAND repair—you will have your emulator back to full functionality within minutes.
Remember: Dolphin is an incredible piece of software that gives new life to classic games. Like any powerful tool, it requires a clean environment to operate. Keep your files organized, your permissions open, and your antivirus configured correctly, and you will rarely see this error again.
Now, go enjoy your games.
If you are seeing the error message "IOS_FS: Failed to write new FST" while using the Dolphin Emulator, it typically indicates that the emulator is being blocked from saving or modifying files in its user directory. This error often pops up during startup or when trying to save game data, and it is usually related to file permissions or interference from security software. What Does This Error Mean?
The "FST" refers to the File System Table, which Dolphin uses to track metadata and access control lists for content stored on the virtual Wii NAND. When Dolphin cannot write this file, it fails to update your virtual console’s internal memory, leading to lost saves or persistent error popups. Common Causes Let’s get to work
Antivirus Interference: Many security suites, including Windows Defender, use a feature called "Controlled Folder Access" that blocks unknown applications from writing to the "Documents" folder where Dolphin defaults its data.
Folder Permissions: The Dolphin folder may be set to "Read-Only," or the user may lack administrative rights to modify files in that directory.
Cloud Syncing Issues: Applications like Microsoft OneDrive often sync the "Documents" folder, which can lock Dolphin's files while they are being uploaded, causing a write failure.
Portable Mode Complications: If you are running Dolphin in "Portable Mode" (with a portable.txt file in the folder), the emulator may struggle if placed in a protected directory like C:\Program Files. How to Fix the "Failed to Write New FST" Error 1. Configure Windows Defender / Antivirus
The most common solution is to allow Dolphin through your security software. The "iOS-FS failed to write new FST" error
Go to Windows Security > Virus & threat protection > Manage settings.
Scroll to Controlled folder access and click Manage Controlled folder access.
Either turn it off entirely or click Allow an app through Controlled folder access and add Dolphin.exe.
Alternatively, add the Dolphin folder to the Exclusions list in your antivirus settings. 2. Run as Administrator
Sometimes the emulator simply lacks the necessary permissions to write to its own folder. Right-click your Dolphin.exe file.
Select Run as administrator. If this stops the error, you can permanently set this by right-clicking the file, going to Properties > Compatibility, and checking Run this program as an administrator. 3. Relocate the User Folder
If OneDrive or folder permissions continue to cause issues, you can move the user data folder out of "Documents".