To correct the allocation issue you can run a Windows built-in shrink operation for the volume that exceeds the disks layout.
- Open Windows Disk Management from Control Panel > Administrative Tools > Computer Management > Disk Management.
- Identify the volume to shrink. Warning message contains the sequential partition number which can be associated with the volume allocated on the disk. In most cases such partition is the last volume in the disk layout.
- Calculate the amount of space to shrink. Warning message displays the size in bytes and shrink operation is calculated in Megabytes, so you have to convert bytes to Megabytes and round the result. Divide the value indicated in the warning by 1048576 and round it to get an integer.
- Right-click the affected volume and choose Shrink Volume. Specify the value you calculated earlier and click Shrink.
- When the shrinking operation completes, re-run the backup job to verify the result.
For example: Warning says Partition 2 exceeds disk 0 layout by 1024000 bytes
According to the Disk Management, Partition 2 is volume C:
Dividing 1024000 by 1048576 and rounding to the integer would give the result of 1 MB.
Preforming a 1MB shrink of the volume C: