“File too large for the destination file system”

When you copy a large PST file to a USB stick, an SD card or an external drive, Windows may stop with:

The file ‘archive.pst’ is too large for the destination file system.

Why it happens

Many USB sticks and memory cards are formatted with FAT32, an old file system that cannot store a single file of 4 GB or more, whatever the free space on the drive. Outlook PST files are often bigger than that: a Unicode PST can grow up to 50 GB (PST size limits).

To check the drive’s format, right-click it in File Explorer and choose Properties: the File system line says FAT32, exFAT or NTFS.

Three ways to copy it anyway

1. Convert the drive to NTFS, keeping its files

Windows can change a FAT32 drive to NTFS without erasing it. Open Command Prompt and run, with your drive’s letter:

convert E: /fs:ntfs

Back up anything important on the drive first. NTFS drives work on every Windows computer; a Mac can read them but not write to them.

2. Reformat the drive as exFAT

exFAT has no practical file-size limit and works on both Windows and Mac. Formatting erases everything on the drive, so copy its files somewhere else first. Right-click the drive, choose Format, pick exFAT, and click Start.

3. Split the PST into parts under 4 GB

If you cannot change the drive, or the file has to go somewhere else with the same limit, make the PST smaller instead. Split PST cuts it into parts that each open in Outlook on their own:

• choose Size only and 2 GB as the largest part, so every part fits on FAT32; or
• split by year, which often gives parts under 4 GB and is easier to browse later.

Every message lands in exactly one part, the preview shows the parts before anything is written, and your original file is never changed. It runs in your browser: nothing is uploaded.

What does not help

• Zipping the PST. Mail compresses only so far, and a ZIP over 4 GB has the same problem.
• Copying it in pieces with another tool. Split archives are not PST files: they have to be joined again before Outlook can open them.

Frequently asked

Is my PST damaged? No. The message is about the drive, not the file. If Outlook itself reports errors when opening it, run the free health check.

Will Outlook open the split parts? Yes. Each part is a normal PST; open it with File › Open & Export › Open Outlook Data File.