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The amount of space for backup files appears to be limited by Windows to approx. 10% of your disk space. How can that be changed? I've put in a second drive which I want to use primarily as backup storage. It is an 80 gig drive and has nothing else on it. I want to backup approx 18 gig from my main drive, but when the back-up is partially complete, I get an error message that says there is not enough room on the drive. I've tried this before in other configurations using Windows98 , Windows2000, and even XP. I always get the same results. Help???

In short, Windows only lets you use approx 10% of your hard drive space for backup files even if there is nothing else on it and even if you have multiple drives. How can I increase the amount of space allowed for backup files?

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Dani AI

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Short answer: this isn’t a mysterious “10% backup cap” built into Backup — it’s the destination file system. On FAT32 a single file cannot exceed about 4 GB, so Windows’ Backup/NTBackup will fill a single .bkf file up to that limit and then report “not enough room” even if the drive still has free space. This is why an empty 40 GB FAT32 disk will stop a large backup near ~4 GB. (learn.microsoft.com)

Why it happens: the built‑in backup writes backups into one (or more) BKF files (or tape). When the active BKF reaches the FAT32 per‑file ceiling the job aborts with the “backup file (.bkf) is too large for this disk”/“end of media” style error. Command‑line backups use the /F parameter to name the output BKF, so the same limit applies there. (learn.microsoft.com)

Practical fixes (preferred order):

  • Put the backup target on NTFS (no 4 GB file limit). Converting a FAT32 partition in place is possible with Windows’ convert utility (back up first, ensure enough free space, run chkdsk if errors). Example: 
convert D: /fs:ntfs

Convert will prompt to schedule if the volume is in use — it’s one of the simplest ways to remove the 4 GB limit. (learn.microsoft.com)

Alternatives and workarounds:

  • Use exFAT or NTFS for large, removable targets when cross‑platform is needed (exFAT supports very large files). (learn.microsoft.com)
  • If reformat/convert isn’t an option, split the backup into multiple .bkf files or run multiple backup jobs (specify different /F output names) so each BKF stays under 4 GB. For scripted backups the NTBackup /F switch is the standard method. (learn.microsoft.com)

Notes/cautions: always verify a copy of critical data before converting or reformatting; convert needs free space to complete; if backups still fail on an NTFS target, check for quotas, compression, or that the “target” is not a special network share with its own limits. This explains and fixes the exact behavior reported and complements ’s reference to Microsoft documentation.

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Member Avatar for estphil

Not sure if this is what you're looking for, but if not please provide more info (OS, backup prog etc):
http://support.microsoft.com/default.aspx?scid=kb;en-us;Q315688

Thanks but not quite what I was looking for. Windows only lets you use approx 10% of your hard drive space for backup files even if there is nothing else on it and even if you have multiple drives. How can I increase the amount of space allowed for backup files?

Member Avatar for Dani

Are you talking about Windows Me and XP's system restore feature (which by default uses about 10% per drive as "back-up"?)

Member Avatar for estphil

No. I'm refering to the use of Windows backup program (start-programs-accessories-systems tools-backup in Win 2K)when backing up one hard disk to another. Actually, I think this applies to other baqckup software as well. When backing up to another hard drive, Windows limits the amount of space available for those backup files to approximately 10% of the receiving hard drive. i.e. Recently I tried to back up approx 5 gig of data to a 40 gig hard drive which had very little data on it. When the program reached approx 4 gig of data, it announced that the hard drive was full and that I needed to insert new media to continue. This is not the first time that I have encountered this situation. Any suggestions?

Member Avatar for aeinstein

this may be of help
8)

Member Avatar for estphil

Thanks for the help. The articles you referenced helped to explain why. Unfortunately, they do not give a way to alter or change the 4 gig limitation. It's hard to understand why Microsoft would perpetuate this limitation throughout the continuing devolpment of the OS. With todays spacious hard drives, it only seems natural to use one as a backup medium; much faster and much more space than tape. You wouldn't by chance know of a way to overcome the 4 gig limitation would you?

Phil Richardson

Member Avatar for aeinstein

I read the link aeinstien posted, it does tell you how to get around the situation: run multiple backup threads. If you don't know how to do that do a search on Microsoft's website under Support/Knowledge Base targeting Windows 2000 and search for "backup" - you'll get 150 replies. If you don't have the patience to scan through the listing try focusing the search with backup wizard and/or backup command line keywords. Asking for assistance is kewl, asking to be spoonfeed is not.

Member Avatar for estphil

I also read how to get around the problem by using multiple backup threads. What I asked for in my previous post was for a lead to a way to alter or change the 4 gig limitation, not get around it nor to be spoonfed. At one time, I remember seeing a reference to this. Perhaps they were refering to multiple backups.
I may have to resort to running multiple backups, but it may be a bit cumbersome for my use. I work in a small office and I want to be able to rapidly back up 5 different computers without going to great expense such as would be necessary with a large tape unit or multipe tape units. Besides, multiple tape units adds the complexity of relying on multipe users to change tapes and verify that backups were completed or require that I have to spend the additional time to do this.

Member Avatar for aeinstein

Ok, so why didn't you say all that to begin with? Both myself and TechTalkGirl asked you for more information - this was the kind of information need in order to try to help troubleshoot a problem. Next time when someone ask for more info please try to be more specific.

Member Avatar for aeinstein

whoa, down fido! :o Ok, youve got a valid point kaynine, so listen-up estphil, but where here to help, not incinerate! keep the questions coming all! 8)

Member Avatar for aeinstein

I wasn't trying to flame estphill, just emphasis the need for proper clarifications. Apologies for any offense taken, as none were intended.

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