How to fix error: unable to write sha1 filename: Input/output error in Git

First, verify your disk isn't failing and check for filesystem errors. Open Command Prompt as Administrator:

:: Check disk for errors (replace C: with your drive letter)
chkdsk C: /f /r

:: For a quick check without repair
chkdsk C:

If errors are found, Windows will schedule a disk check on the next restart. You can also check disk health using:

# Check S.M.A.R.T. status in PowerShell
Get-PhysicalDisk | Select-Object FriendlyName, MediaType, HealthStatus

# Or use wmic
wmic diskdrive get status

If the disk shows "Warning" or "Unhealthy" status, back up your data immediately and replace the drive.

NTFS compression can interfere with Git's object file creation. Disable it on your repository folder:

Using File Explorer:
1. Right-click on your repository folder
2. Select "Properties"
3. Click "Advanced..."
4. Uncheck "Compress contents to save disk space"
5. Click OK and apply to all subfolders and files

Using Command Prompt (as Administrator):

:: Navigate to the parent directory of your repo
cd C:\Users\YourName\Projects

:: Remove compression from the repository folder
compact /u /s /a /i "your-repo"

After disabling compression, try your Git operation again.

Antivirus software often scans files as they're created, which can conflict with Git's rapid object file creation. Temporarily disable real-time protection:

Windows Defender:
1. Open Windows Security
2. Go to "Virus & threat protection"
3. Click "Manage settings" under "Virus & threat protection settings"
4. Toggle off "Real-time protection"
5. Run your Git command
6. Re-enable real-time protection immediately after

Better long-term solution: Add exclusions for Git directories:

C:\Users\YourName\Projects
C:\Program Files\Git
%USERPROFILE%\.gitconfig

For Windows Defender, add folder exclusions in Windows Security > Virus & threat protection > Manage settings > Exclusions.

Verify you have adequate free space. Git needs space to create temporary files and object files:

# Check available space
Get-PSDrive C | Select-Object Used, Free

# Or in Command Prompt
fsutil volume diskfree C:

If space is low, clean up:
- Run Disk Cleanup (cleanmgr.exe)
- Clear npm cache: npm cache clean --force
- Remove unused Docker images: docker system prune -a
- Delete old Git branches: git remote prune origin

Also check for disk quotas if you're on a corporate machine:

fsutil quota query C:

If the repository has accumulated corrupt or incomplete objects, clean it up:

# Verify repository integrity
git fsck --full

# Remove loose objects and pack repository
git gc --prune=now

# Aggressive cleanup (use with caution)
git gc --aggressive --prune=now

# Repack all objects
git repack -a -d -f

If git fsck reports corrupted objects, you may need to fetch fresh copies:

# Remove any corrupt loose objects (empty files)
# PowerShell command to find empty files in .git/objects:
Get-ChildItem -Path .git/objects -Recurse -File | Where-Object { $_.Length -eq 0 } | Remove-Item

# Then fetch from remote
git fetch --all

If your repository is on a network drive (mapped drive, UNC path, or cloud-synced folder), move it to a local drive:

:: Copy repository to local drive
xcopy /E /H /K "\\server\share\repo" "C:\Projects\repo\"

:: Or using robocopy for better reliability
robocopy "Z:\repo" "C:\Projects\repo" /E /COPYALL /R:3 /W:5

Avoid these locations for Git repositories:
- OneDrive, Google Drive, or Dropbox synced folders
- Network mapped drives
- External USB drives (unless stable)

After moving, update any IDE workspace settings to point to the new location.

If you dual-boot Windows with Linux, Windows Fast Startup can leave NTFS in a hibernated state, causing write errors when accessed from Linux:

:: Disable Fast Startup via Command Prompt (as Administrator)
powercfg /hibernate off

Or via Control Panel:
1. Open Control Panel > Power Options
2. Click "Choose what the power buttons do"
3. Click "Change settings that are currently unavailable"
4. Uncheck "Turn on fast startup"
5. Save changes

After disabling, fully shut down Windows (not restart) before accessing the drive from Linux.

If the repository remains corrupted after other fixes, clone a fresh copy:

# Back up any uncommitted changes
git stash
git stash show -p > my-changes.patch

# Clone fresh to a new directory
cd ..
git clone <remote-url> repo-fresh

# Apply your changes to the fresh clone
cd repo-fresh
git apply ../repo/my-changes.patch

If you have committed changes that haven't been pushed:

# In the old repo, create a bundle of unpushed commits
git bundle create ../unpushed.bundle origin/main..HEAD

# In the fresh clone, apply the bundle
git fetch ../unpushed.bundle main:temp-branch
git merge temp-branch

Delete the old corrupted repository only after verifying the fresh clone works correctly.