I fixed it. I got the diagnostic USB cable out of the box and hooked it up to my laptop, and chkdsk discovered several corrupt attribute list entries, which it fixed. I then ran another pass of chkdsk, and it found free space marked as allocated, which it also fixed. The third run of chkdsk came back clean, so I rebooted the TViX in normal mode and tried the native disk check again, and this time it worked.
I guess the moral of the story is to make sure you run the disk check on a regular basis, and if it doesn't complete successfully, check the drive in a PC. I guess the disk check either isn't using a full copy of fsck, or fsck is only able to confirm that an NTFS drive has no errors and isn't able to fix anything if the drive isn't clean. I've made a habit of purging old files and running a disk check on a weekly basis, and this is the first time in five years of use that anything has gone wrong, and it wasn't wrong for more than a day at most. It's possible that continuing to make new recordings could cause data loss if you allow the TViX to continue operating with a bad filesystem, I suppose.
I wasn't able to check the SMART status of the drive, as you can't get SMART data over USB, and it would be a pain to remove the HDD from the DVR, open my desktop, connect it, check it, and then transplant it back into the DVR again. That will have to wait until another time.
It seems that smartmontools is able to query at least some USB drives. It might be worth a test.
Last edited by Aleron Ives; 07-18-2017 at 04:42 PM.