Challenge
A job or task reports the error:
There is not enough space on the disk
Cause
This error is relayed by Veeam Backup & Replication when the underlying system reports the error while attempting to write a file.
More often than not, this error quite literally means the disk has insufficient free space.
However, if it can be determined that the disk Veeam Backup & Replication was attempting to write to has sufficient free space, the issue may instead be related to a filesystem limitation or a configured disk quota. File system limits, file system quotas, or network share quotas can trigger this error.
If the error is due to a file size limit, the job will always fail after transferring the same amount of data.
If the error is due to a quota, subsequent job sessions will typically fail without transferring any data.
Solution
Identify what file Veeam Backup & Replication was attempting to create/write when the error occurred.
Check if that disk has sufficient free space.
Check if there is a filesystem single file size limitation.
Check if a disk quota is configured.
More Information
TechNet: NTFS Disk Quotas