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Discussion Starter · #1 ·
Windows Backup fails with error "unable to write backup files to external drive Q:" message. The primary reason for the backup is multiple large company files in Quickbooks, hence the "Q" drive letter. I've checked other threads and nothing suggested there seems to be relevant to this issue.

It was working up to two weeks ago, running with an every day at 11PM schedule. The Q: drive is a 7 month old 3TB WD with 2.05TB free which tests out as healthy. All files can be accessed on the backup drive up until the date when the backups began to fail to complete.

Specs:
HP EliteBook 840 G1 Laptop


  • Windows 7 Professional 64
  • Intel® Core™ i5-4210U with Intel HD Graphics 4400 (1.7 GHz, up to 2.7 GHz with Intel Turbo Boost Technology, 3 MB cache, 2 cores)
  • 8 GB 1600 MHz DDR3 SDRAM (2 x 4 GB)
  • 14" diagonal HD+ SVA anti-glare flat LED-backlit (1600 x 1900)
  • 180GB SSD

Product# J5Q17UT#ABA
 

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If the backup drive Q: is formatted FAT32 instead of NTFS, then you would not be able to copy files larger then 4GB
Being a 3TB drive, it should be initialized as GPT instead of MBR. Any drive larger then 2.2TB must be initialized as GPT.
Run Check Disk on the Q: drive. Go to Start/Search and type CMD, Right click the CMD results and Run As Administrator. In the Elevated Command Prompt type the drive letter for the drive (eg) Q: and press enter. (eg) Q:\> at this prompt type chkdsk /F and press enter. Now type a Y for Yes to Unmount the drive. Check Disk will go through 3 stages.
 

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Discussion Starter · #3 ·
Eureka moment! :facepalm:

I was reading up on Windows Backup and discovered that it must create an 'interim files cache' ON THE SOURCE DRIVE before copying the backup files to the destination. I believe I had read this somewhere in the distant past, but it did not register until I re-read the MS documentation.

The files to be backed up encompassed some 54GB of data, while there was only 10.2GB of free space on the source drive! Of course, the 'interim files' could not be cached in that space, so the backup failed. I found that the secretary had placed a large backup of her entire photo collection temporarily on the office system drive, reducing the available free space to that puny level. After moving her photos over to the backup drive, the backup process ran and completed with no errors!

This can be an object lesson for anyone who uses Windows Backup (including myself) that certain criteria must be met for many utilities to function properly. There must be enough free space on the source drive to duplicate ALL the files to be backed up when using Windows Backup.

Thank you spunk.funk for your insightful and detailed response, most of which I had already tried before posting this thread. :thanx:

I wish all on TSF a happy and prosperous New Year. :beerchug: :partytime
 
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