Steam disk write error

On screen: An error occurred while updating <game> (disk write error)

What it actually means

Steam could not write or rename a file inside steamapps/downloading or steamapps/common. It is a local write failure, not a download problem.

The usual causes are NTFS permissions on the library folder or a read-only attribute, a stuck zero-byte or locked file left behind by an interrupted download, antivirus or Windows Controlled Folder Access blocking Steam.exe from writing, a full disk, bad sectors, a failing SSD, or a library sitting on exFAT or a network share.

How to tell which one you have

This is almost always local. The server-side equivalent looks different — Steam says content servers unreachable when the problem is on their end.

Fixes, in the order worth trying

1. Open Steam's own content log — In your Steam folder, open logs\\content_log.txt and search for “failed”. It names the exact file and the operating system error code. No guide on the first page of results tells you to do this, and it turns a guessing game into a two-minute fix.
2. Use Repair Folder — Steam, then Settings, Storage, pick the drive, the three-dot menu, Repair Folder. This is Valve's own tool and it fixes the permissions case.
3. Delete zero-byte files — Look in steamapps/common/<game> and steamapps/downloading for files of 0 KB and remove them.
4. Clear the download cache — Settings, Downloads, Clear Download Cache. Cheap and occasionally decisive.
5. Exclude the Steam folder from antivirus and turn off Controlled Folder Access — Windows ransomware protection blocks Steam writes silently and is a common cause on otherwise healthy machines.
6. Verify integrity of game files — Right-click the game, Properties, Installed Files.
7. Run chkdsk and check SMART data — If the log points at different files each time, suspect the drive.
8. Move the library to another drive — The definitive hardware test. If it installs cleanly elsewhere, the original drive is the problem.

Operator documentation: help.steampowered.com. Valve's page covers update and installation issues generally: “The error results when Steam is not able to complete the installation. The specific reason for the error will be shown in the parenthesis at the end of the error message.” The older widely-shared support.steampowered.com link now redirects here.

Common questions