Accessing Photo Files On Multiple Drives In Lightroom

You will find the media containing all the images you have imported to Lightroom in the 'Folders' panel of the Library module.
In my screen shot illustration note that 'Macintosh HD2' is currently online and ready to work with. You can tell because the small status-box adjacent to its name is lit green.

However, the 'PICTURES' volume, an external archive hard drive with images that are a part of my catalog is currently offline. The status-box is not lit. 'PICTURES' is either turned off or is not connected to my workstation.

Now look to the last volume in my 'Folders' panel, 'Rick Gayle/Girl Scouts proj'. This CD and its contents was imported to Lightroom so I could review photos of urban shopping environments I scouted for a client's photo shoot. I pulled together a few of my old location files here to easily build a simple, yet impressive-looking web gallery for another client doing research as part of a project bid.

But NOTE the status box adjacent to its name. It's glowing red!

This means that this volume (the CD) is mounted on my workstation's optical drive and that the images are accessible to me, but that red color in the status-box alerts me to the fact that even though Lightroom will allow me to make image edits within the Develop module – or to add keywords and rating tags to images – Lightroom will not be able to write these changes into these CD-stored images' metadata! (SEE illustration below.)

Lightroom will still write these changes into its database (the Catalog), all I've done to these photo files within the application itself. However, these changes cannot be seen within Adobe Bridge or another raw file-converter application. Lightroom is unable to write changes to metadata onto my archive CD: