guide · backup
“Is everything really on the NAS, and is it the same?” A backup that finished without an error message is not the same as a backup you have looked at. Diffoniq compares the original folder with its copy — on a NAS, a file server or a USB drive — and shows what is missing, what is extra and what differs. Then it puts the answer into a report you can keep.
If the backup sits on a NAS or a file server, you do not need to map a drive letter. Give Diffoniq the original and the network path directly:
"C:\Program Files\Diffoniq\Diffoniq.exe" "D:\work" "\\nas\backup\work"
Or press Ctrl+O in Diffoniq and enter the two folders as left and right path (the File… buttons open a browse dialog). The path above is the installer’s; if you use the portable ZIP, put in the folder you unpacked it to.
Many backup and copy tools give the copy a new modification date. If dates decide, every such file looks changed and its contents are never read. For a backup the question is a different one: are the two trees the same, no matter when the files were written?
So open Options → Directory Comparison… and check that Ignore Date and Ignore Time are both on, and Look In Subfolders as well. Then size and contents decide: files of the same size are read on both sides in the background and compared by a content checksum. The progress bars in the rows show that work.
Every file that is not identical ends up in one of four states:
| State | What it means for the backup |
|---|---|
| only left | In the original, missing from the backup |
| only right | Only in the backup — deleted from the original since, or never there |
| different | On both sides, but not the same |
| unverified | Same size, but the content check had not finished (or you stopped it with Esc). Never counted as identical |
A report counts the identical files and lists only the rest, so what you read is the list of problems. Double-click a text file to see the lines that differ.
File → Export Report… writes what is on screen into a single HTML page, a text file or JSON. The header names both folders and the options the comparison ran with, so the report explains itself later. Nothing on either side is changed.
The same check runs without a window, for example every morning from the Task Scheduler:
schtasks /create /tn "Nightly change report" /sc daily /st 06:00 ^ /tr "\"C:\Program Files\Diffoniq\Diffoniq.exe\" /report D:\work \\nas\backup\work --out D:\reports\work.html --content"
Keep --content in the command. Without it the headless report does not
read file contents, and two files of the same size count as identical. In a batch file,
wait for the report with start "" /wait; the exit code says what happened:
| Exit code | Meaning |
|---|---|
0 | Report written, no differences |
1 | Report written, differences found |
2 | The report file could not be written |
3 | Invalid arguments, or the comparison failed |
Diffoniq remembers the checksums it has computed. On the next comparison, a file whose size and modification time are unchanged is not read again; its checksum comes from that memory. That is why a second check of a large backup is so much quicker than the first.
The price: if a file on the backup changes while its size and date stay the same, a repeat check still reports it as identical — the scheduled report included. Some backup and sync tools restore dates this way, and a failing disk does not announce itself either. To read every file again, open the comparison in the window and press Ctrl+F5 (Re-verify Contents). Do that now and then, and always before you delete the original and rely on the backup alone.
The full reference is in the help: Comparison Reports, Content Hash Cache and comparing over the network.
Diffoniq runs on Windows 10 and 11, 64-bit. Every feature is available for 30 days before you decide.