Acronis backup has consistent write failure at ~5GB of 45GB when backing up to a 1TB HDD. Why? There is no problem writing files from Windows Explorer or downloading huge star catalogs, for example.
I guess it's possible HP has formatted it differntly. However, there are two drives in the HP Media Vault network storage box, both apparently formatted by HP the same way. The original drive is 300GB and Acronis backs up to that drive with no issues. I added the 1TB. Everything else will write to either drive. I cut and paste files from the 300GB drive to the 1TB drive so as to make room for the Acronis backups.