Directory/folder availability check

[Dan_W]

Hello,

I am quite a new user, probably a stupid question, I have a real-time sync set up that performs a mirror of my local computer C:\ Drive Documents folder on a to a NAS, I would like to understand in the event when this real-time sync runs not all the folders in the source directory can be seen (say a local C:\ drive folder corruption) what prevents FreeFileSync from assuming those files have been deleted and therefore deleting them on my NAS also thereby losing the data?

Many thanks.

Dan

[xCSxXenon]

Good concern to have, as FFS will absolutely copy corrupted data just as well as good data. If a monitored location can't be seen at all, RTS will never start a sync anyway, so no worry there. There is no concrete answer to your question, because as always, "it depends". Why would "not all the folders in the source directory" be seen, as you say? If it's because of a classic "Directory is corrupt or unreadable" from Windows, FFS doesn't see that as a deletion and the destination will be untouched. If it's because a mountpoint or hardlink existed in a location and no longer exists or the attached resource doesn't respond, it's possible that the data will be considered "not there" and FFS will mirror that to the destination.

Ultimately, you need to identify actual scenarios for which you are at risk and have a backup solution to no longer be at risk. Been in the business a while, I can't think of any common reason that some data may not show up when it wasn't deleted somehow. This article explains the faults with a 3-2-1 backup, but a 3-2-1 backup is more than most people actually need and more than most already have anyway.
https://www.unitrends.com/blog/3-2-1-backup-sucks#:~:text=The%203%2D2%2D1%20backup%20strategy%20simply%20states%20that%20you,off%2Dsite%20for%20disaster%20recovery

[therube]

can't think of any common reason that some data may not show up when it wasn't deleted somehow

Ransomware.
(Beside physically changing file contents), often will rename the file *.encrypt.

[xCSxXenon]

can't think of any common reason that some data may not show up when it wasn't deleted somehow

Ransomware.
(Beside physically changing file contents), often will rename the file *.encrypt.

Sure but that is not "data not showing up". That is a different, but valid, concern than what was proposed

[Dan_W]

Many thanks to each of you for the replies, I don't have a specific scenario I'm afraid, I just have a recollection of a failure mode we encountered at my work where we were using a UNIX based mirroring system between two countries overnight, and where a WAN connection was lost overnight the mirror tool interpreted this as data being deleted (because it could not see the data) and promptly deleted the data on the destination site, but again this was some years ago with no doubt less sophisticated software, so I was just wondering if any specific protections are in place now on more modern software. Again many thanks for taking the time to reply.

[Dan_W]

Thanks Friezer, I was coming to the same conclusion, convenient though it is to have real-time, if there is not a specific protection I'll just run the batch as needed. Many thanks.

[Zenju]

Just some clarifications:

There is no such thing as "not all files/folders are seen" without also an error indication, in which case FFS will fail syncing these items and not delete from the target.

The more likely case is that you (the user) are making a mistake and accidentally deleting or corrupting files on source. The proper solution for this is to either set up the recycle bin or versioning to at least allow to undo the damage.

[Dan_W]

Just to be clear I have not lost or deleted anything, and I already have a recycle bin setup on my NAS, I was merely asking a hypothetical question to try to understand how the software works. So if I understand your reply FFS will see an error and not perform the mirror operation, in which case that is the answer I was hoping for >> many thanks.