Does External USB Copy Verify Files?

[DigitalOxygen.ca]

Does the copy operation under External Backup > External Drive do any kind of verification when copying the files?

[Sarsfield]

You can set the file verification (check file contents) when setting up the copy job. It probably lengthens the time appreciably but I have never tried it.

[DigitalOxygen.ca]

Are you sure that option is for verification and not comparison?

[doktornotor]

No, of course not. Why should it? It's copy.

[DigitalOxygen.ca]

Fair enough I suppose. The wording "check file contents" doesn't make it very clear though. Things like that shouldn't be left up to assumptions or wordplay. It should be phrased something like "verify copied files"

[doktornotor]

That's not what the option does, you completely misunderstood the reply. See man rsync(1)

Note that rsync always verifies that each transferred file was correctly reconstructed on the receiving side by checking a whole-file checksum that is generated as the file is transferred, but that automatic after-the-transfer verification has nothing to do with this option's before-the-transfer "Does this file need to be updated?" check.

With --checksum, rsync will use a checksum in addition - as opposed to just filesize/timestamp/mode/owner - to determine what's needs to be updated at the destination, before the transfer.

[DigitalOxygen.ca]

No, I understood the reply, I was just distracted when formulating mine and made a mistake

So the short answer is: Yes, the Copy operation verifies files by default.

This would also be somewhat clearer if it was more clearly stated that the Copy operation actually uses rsync. Based on it's name it sounds more like it uses the cp command or something else. Had I known it used rsync I never would have asked the question because I aware of rsync's default write verification functionality.

Also, verification and comparison are not the same. When you said "You can set the file verification (check file contents) when setting up the copy job." That was misleading. It seems you were speaking of the comparison of the file contents done up front to determine if the file should be copied.

[doktornotor]

When you said "You can set the file verification (check file contents) when setting up the copy job." That was misleading. It seems you were speaking of the comparison of the file contents done up front to determine if the file should be copied.

That wasn't me in the first place...

[DigitalOxygen.ca]

Huh, well look at that. The way the replies flowed together it just seemed like it was. I honestly didn't look at the usernames that time.

[jfneuch]

Hello,
In the latest firmware (4.2.2 20160901), there is no more choice to verify or not before copying.
Does anyone know if the fonction copy inclue md5 cheksum ?
Thank very much to whom who take time to answer me
Jean

[sjohund]

Why nobody answer? Is there anybody?

[DigitalOxygen.ca]

I got this response from support way back in 2016. Haven't used that feature in a long time so can't comment on the missing verify option.

QNAP: There's no check sum for rsync or NAS to NAS either. However, there's file level block check after data coped to destination.

Me: So when you say "file level block check" does that mean that it verifies each block was written correctly to the destination (i.e. reads it back)?

QNAP: Yes, it compares the blocks between source and destination to make sure data has been synchronized to destination correctly.