If you put the OS on a smaller SSD, you'd want to have all the "My ....." folders linked to folders on your larger slower HDD. One advantage is if the OS gets messed up, you still have all your files available on the other drive, which makes it safer to reload or upgrade the OS, if needed. Linux does this using different partition or one on a different drive for the "home" folder where all personal data goes. I find that approach easier, and safer.
At present, I have system on 160 GB drive, Samsung, that had been working well for past 10 years. But it can no more keep 200 GB data files (documents, downloads, music, pictures, videos). So, I keep them on 1 TB Western Digital which is about 3 yr old. The problem is: I have to re-direct/move data folders from 160 GB drive to 1 TB drive by going to Location tab under Properties.
It seems Windows is designed to store data on the same drive where OS is installed. Now, this re-directing may be an interference with Windows native system. Besides, it has its own limitations. When it comes to redirecting OneDrive or Dropbox, it poses some hurdles.
Under these circumstances-- OS on one physical drive and Data on another-- would be a good idea or bad idea? Is it best to keep OS and Data on same physical drive, as Windows may have been primarily designed, or keeping OS and Data on separate physical drives make access to system and/or data faster?
Is it better to replace good old, loyal, Samsung 160 GB with a new 1 TB drive (Western Digital or Seagate?) and use it for OS + Data? Then, use 160 GB and 500 GB Portable for backups?

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