How can I edit lightroom 5 smart previews on mac book pro (mbp) when the lightroom 5 master image files are on my external hard drive is disconnected from the mbp

Question

How can I edit lightroom 5 smart previews on mac book pro (mbp) when the lightroom 5 master image files are on my external hard drive is disconnected from the mbp? So far when I try to disconnect the external HD from the mbp, I get the following pop up window: The disk "external hard drive A" couldn't be ejected because "Lightroom" is using it. Quit that application and try to eject this disk again. When I do that and restart Lightroom 5, the Adobe Photoshop Lightroom - Select Catalog screen pops up but doesn't list my external hard drive A as a choice.
I've reviewed Adobe's Lightroom Help | Smart Previews Lightroom 5 web page and still haven't been able to figure what I'm doing wrong. Any help would be appreciated.

Answer 1

Your internal HDD. by default, is named 'Macintosh HD'. From what information you supplied, it looks like there is already a Lightroom catalog installed on you local (internal) HDD using the standard naming convention Adobe uses as well as a Lightroom catalog on your external drive which you created. To be sure of which catalog Lightroom is loading when it starts up, To do this, start Lightroom as you normally would. After it starts, select the Lightroom menu item, then select the Catalog Preferences item and finally, navigate to the General tab. The Location information will tell you exactly what catalog Lightroom is opening by default. This will likely be the Photography Mac Book Pro Versions catalog on your external HDD. Once that is confirmed, you are ready to proceed. As an additional test/verification, you can shut down Lightroom and, this time, start Lightroom while holding down the ALT/OPTION key. This will cause Lightroom to pause and display a screen which will allow you to chose a different catalog to open. Navigate to the /Users/[user name]/Pictures/Lightroom folder and select the Lightroom 5 Catalog.lrcat file. When Lightroom comes up, there should be no previews or folders as this catalog should be empty. Now you can be certain which catalog is being used and which catalog has all your data and you are ready to migrate your current catalog. Shut down Lightroom.
To migrate your current catalog, use Finder to locate your Photography Mac Book Pro Versions folder on your external drive. Select the folder and select COPY from the context menu. Next, use Finder to navigate to the /Users/[user name]/Pictures/Lightroom folder on you internal HDD. You can start at the Macintosh HD level and work your way down by opening each level (Macintosh HD/Users/[user name]/Pictures). Select the /Pictures folder and then select PASTE... from the context menu. When the COPY/PASTE is complete, you should see the following files on the Macintosh HD:
Macintosh HD/Users/[user name]/Pictures/Lightroom/ and
Macintosh HD/Users/[user name]/Pictures/Photography Mac Book Pro Versions
The Macintosh HD/Users/[user name]/Pictures/Lightroom folder will contain the empty default catalog the Adobe created when Lightroom was installed and Macintosh HD/Users/[user name]/Pictures/Photography Mac Book Pro Versions will contain a copy of the catalog you created on your external HDD.
You are almost done now. Make sure your external drive is still attached for this step. Restart Lightroom using the ALT/OPTION key again. When the Select Catalog screen appears, select the Choose a Different Catalog button (lower left side). When you do, a Finder window will open to allow you to navigate to a catalog of your choosing. Navigate to Macintosh HD/Users/[user name]/Pictures/Photography Mac Book Pro Versions and select the file Photography Mac Book Pro Version.lrcat. This is the copy you just created. Select the Open button and Lightroom should start. You should see all of your previews and settings just as before. Also, in the left hand panel, all of your folder should show up and none of them should be dimmed and none of your previews should display a small exclamation point badge. Either a dimmed folder name or an exclamation point badge indicates that Lightroom can't find the associated image file. If everything looks good, go to the Lightroom menu, select Preferences and then select the General tab. Under Default Catalog, select an option to either load the LAST catalog opened or select the Users/[user name]/Pictures/Photography Mac Book Pro Versions catalog from the drop down. Shut down Lightroom and then restart it normally. This time, when Lightroom starts, you should be viewing the new copy of your catalog. You can confirm this by looking at the General tab on the Catalog Preferences screen (Lightroom/Catalog Preferences menu items). Shut down Lightroom once again and this time, eject your external drive before restarting. This time, your folders in the left hand panel will be dimmed but you should be able to work with your smart previews. If Lightroom should display a Select Catalog screen with the external drive detached, double check your settings as it indicates Lightroom is still looking at the copy of the catalog on the external drive rather than the new copy you made.
Finally, if you are seeing dimmed folders and/or exclamation point badges with the external drive attached, this indicates a problem. You can select any folder and select Update Folder Location from the context menu. This will allow you to navigate to the copy on the external drive and select it. Lightroom will then update the catalog (select to synchronize the content). This will not only clear the dimmed folder problem but also remove the exclamation point badges for all photos in that missing folder. However, it may indicate that not all went well with the copy of the catalog so make sure to verify all went well. You can use the Get Info option on the two folders. You should see the same number of files/folders for both the copy on the internal drive as well as on the external drive but you can't rely on the byte count because of the possibility of differences between the geometry of the two drives. Hope this all helps!