ubuntu – Rsync : Preserve date after copying

I have an issue with files attributes since I changed my company’s file system from an old ubuntu 12 to a Synology NAS.

I initially mounted NFS shares on my old file system, then with cp I copied everything, everything was ok But i forgot to preserve the attributes, and we lost especially the date, the dates became the copy date, and not the real date.

I found the rsync command rsync -vrt –size-only /src /dest But some files have been modified since the copy, and the command overwrite them…

For example i tried to create a file on the old file system, copying it on the new synology then modifiyng the file on synology. When i use rsync, the file is erased and replaced by an old version.

I am looking for a command, to copy timestamps for files only when the file have exactly the same size (haven’t been modified)

No mater if it takes long time

Thanks