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Learn How to Backup Large PST Files in Few Steps ?

backup large pst files

Outlook always generate the error of “cannot backup large .pst files” or PST size increased/exceeded when the PST size is more than the standard size limit for back up. We assume that large size of PST is the only cause for this kind of error.


Although it is, but not only the large PST size is always the point of conflict, there are a lot of other points too which led Outlook to generate this kind of error. This blog is to fix the error depicting cannot backup large Outlook PST file.

User Query to Backup Large Outlook PST File

User's issues are often like this: -

“My Outlook is continuously popping error that cannot backup large outlook pst file. There is no space in your external drive to back up the files. But I have 20GB of space in my external storage and the PST I want to backup is of only 5GB. How is this possible? Please suggest a solution for how to backup large PST files.”

Which file system are you using?

The technicality used here is your File system. File system comes with the maximum file size which repel all the files if exceeding its maximum file size. Now it depends on your system that at which file system it works.

FAT32 as this is the general file system tied up with your system. Well if you are using FAT32 then your maximum cluster size is of only 4GB as it is the standard file size limit of FAT file system. There is a DIY solution to this issue, switch your file system to NTFS. Because it supports very large file size, approximately up to 16 billion bytes in file size.

How to convert FAT into NTFS?

Follow the simple procedure to convert your current file system in NTFS: -

  • Open Command Prompt or press Windows + R and type cmd.
  • Now type convert b: /fs:ntfs
  • Your file system gets converted in NTFS easily. Exit command prompt.

Points To Be Noted

Well before switching your File System, read properly the undermentioned points and do follow.

  • Point 1 :- The b: in the syntax is your local drive. So replace it with the drive letter of your external storage drive.
  • Point 2 :- The windows vista, Windows 7 & windows 8 user must follow these steps to access command prompt or the syntax won’t work.
    • Go to Menu
    • Right click on Command Prompt
    • Then click Run AS Administrator
    • Confirm the alert message and pass the administrator credentials if asked

    divide large pst file

  • Point 3 :- For confirming your current File system.
    • Right click in Driver Explorer
    • click on Properties > Check your File System

    backup large outlook pst file

  • Point 4 :- Windows previous version like 95, 98, NT can’t read NTFS while other versions are compatible to NTFS file system.
  • Point 5 :- Open MS Outlook and paste the app password obtained when being prompted for password
  • STEP 7 :- Once the password is updated, MS Outlook will be able to connect to Gmail again with the 2-step verification enabled for the account.

DIY Solution to Backup Large PST Files

With this manual approach users can easily backup large Outlook PST files by following some useful steps-

  • Delete the irrelevant data meanwhile you can remove the deleted folder, empty folder etc.
  • Archive your data file.
  • File > Account setting
  • Data Files > click Add
  • Rename > Click OK

Your archive data file is in another location from your PST file. You can open your archive files anytime by importing Outlook Data File in Outlook.

Compact your data file by adjusting the setting

  • Right Click on the PST you want to Compact
  • Click Data File properties
  • There will be an Advanced Tab > Click Compact now
  • Your PST file get Compacted

These all measures should resolve your issue. Even if you cannot backup large PST files then refer to next section.

Upshot – Cannot Backup Large Outlook PST File

The error "cannot backup large PST files" will get resolved by the above described method and you can copy large PST files easily. Well if your issue persists then I would recommend you to use third party tool i.e. Outlook PST Splitter software. This tool easily split your PST files and backup them. Split PSTs consist the same data but in compressed size so may the size issue get resolved with splitting. You can opt this solution too.

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