Cannot connect to iTunes Media folder located on another volume during sync.

There are several things you need to clarified to understand your current situation. The iTunes library file is a database that keeps track of you iTunes media. It defines your iTunes library. It is usually called iTunes Library.itl. The iTunes folder (in your startup disk user account Music folder) is the default location for iTunes Library.itl file.

Then, there is your iTunes Media folder. By default, this folder contains all of your actual iTunes media files, organized by iTunes into subfolders by media type, artist, and album. The default location for the iTunes Media folder is also in your iTunes folder (in your startup disk user account Music folder).

One common option to move your iTunes data off of the startup disk is to put your iTunes Media folder on an external drive (or network storage) while keeping the iTunes Library.itl file on your startup disk at the default location. To do this without iTunes losing track of your media files (where they are located), put an empty iTunes Media folder at the target location. Change the location of the designated iTunes Media folder in iTunes preferences Advanced pane to point to the new iTunes Media folder. Then give the "consolidate library" command to have iTunes copy your media files and organize them into the new iTunes Media folder location. This command is at menu bar -> File -> Library -> Organize Library -> Consolidate files (checkbox).

NOTE: In iTunes preferences Advanced pane, the TWO checkboxes for Keep iTunes Media folder organized AND Copy files to iTunes Media folder when adding to library should be checked (unless you have a specific reason for not doing so).

The OTHER common option is to manually copy (using Finder) your entire iTunes folder (with the iTunes Library.itl file and iTunes Media folder) to the external drive or network storage. Then, use the option to open a different iTunes library

Open a different iTunes Library file or create a new one - Apple Support

to select the iTunes Library.itl file at the new location.

The key difference is the location of the iTunes Library.itl file. The iTunes Library.itl is frequently accessed and updated by iTunes. If it is located on network storage (with much slower access speed compared to a directly connected drive), it can adversely affect the performance of iTunes. Therefore, the first option described above may be preferable, to keep the iTunes Library.itl file on the internal drive while storing the media files on network storage.

In your situation, which setup for iTunes is being used?

For some reason, when I wrote my reply, I was thinking your iTunes data was on network storage, but you did say "RAID." Sorry about that... 🙂 If it's on a RAID, the specific option used is not as critical. And you put the entire iTunes folder on the RAID, if I understand correctly. Having the iTunes Music folder structure (instead of iTunes Media) is the "old way," but don't see how that would result in the described problem...

So, the actual stated problem is not being able to sync your iPhone? When you run iTunes (on the Mac), are you able to access your current iTunes library (on the RAID) and play your media files? If you can, it seems like you should figure out why the iPhone does not sync to your current iTunes library, not create a new library.

Did your iPhone previously sync properly with your iTunes library, using latest iTunes under OS X 10.10.5? It's not clear to me if this worked before and does not work now for some reason, or if this system config is something new (recently upgraded from your 10.8.5 system).

But when I look at my phone, over half of the Music Albums I have selected in the Music panel on my "device" (iPhone 5), don't transfer to my iPhone.

Are you sure those song files are located on the RAID? Songs purchased from the iTunes Store can appear in your iTunes music library, even if they are not stored locally. You may be accessing them (purchased songs) from Apple's servers ("iCloud"). And if you have an iCloud Music Library, all of your songs can be seen from iCloud. Song files must be stored locally for iTunes to sync them directly to a connected device. To check, do a Get Info on a song (that does not sync) in iTunes; on the Info window's File tab, look at Location.

How about I create a new library on my system drive, import them (and the playlist) into the library...

You don't need to do those steps you described, if you want to start off with a new iTunes library and add your media files. Use this procedure to create a new (blank) iTunes library at the desired location, such as on the RAID.

Open a different iTunes Library file or create a new one - Apple Support

In the new library, open iTunes preferences Advanced pane, to confirm the designated iTunes Media folder location is within the iTunes folder that holds the iTunes Library file. Also confirm that the TWO checkboxes for Keep iTunes Media folder organized AND Copy files to iTunes Media folder when adding to library are BOTH checked.

Then, from the menu bar, File -> Add to Library, and select the old iTunes Music folder where all of your media files are currently located. iTunes will import all media files it finds there into your new iTunes library, and put a copy of files in the designated iTunes Media folder, organized into subfolders by media type, artist, and album. This is a copy (not a move); after confirming all of your media is there in you new iTunes library, delete the now duplicated files to free up the space.

== Error -54 ==

From an OS9 reference, error -54 is a software lock on a file or a permissions error. (Although there is no formal list of OSX error code some of the old codes still apply to OSX .)

First, try simply restarting your computer.

Try quitting iTunes, then deleting the .xml (not .itl !) version of the library file in the iTunes folder (iTunes will generate a new one).

iTunes Library cannot be saved (Error -54) - https://discussions.apple.com/thread/1912814 - various things to try.

Unknown error (-54) while syncing ipod - https://discussions.apple.com/thread/1082953 - problem was locked files

Why does iTunes keep showing a -54 error when I sync my iPad? - https://discussions.apple.com/thread/3727114

Error -54 possibly related to Touch Copy - https://discussions.apple.com/thread/3727114 - cleared by deleting preferences on iPad.

iTunes: Missing folder or incorrect permissions may prevent authorization - http://support.apple.com/kb/ts1277 = https://web.archive.org/web/20140730222128/http://support.apple.com/kb/ts1277

Troubleshooting permissions issues in Mac OS X - http://support.apple.com/kb/HT2963

Some song files may be corrupted. Repairing permissions does not do anything to the song files. Doing a Repair (or Verify) on the First Aid tab, with the RAID volume selected in the Disk Utility sidebar, may be relevant to the overall health of the volume, although it won't fix individual files.

Show one of those song files in a Finder window. Right-click it and select Open With -> iTunes. Are you able to add the song file that way? Does it start playing in iTunes?

If you cannot add that individual song, right-click it and select Open With -> QuickTime Player. Does it open in QuickTime Player and let you play it?

If the song plays fine in iTunes, doesn't that mean the song was add to your iTunes library?

iTunes organizes the imported song files based on the song's "metadata" (the imbedded info in the song file for things like song name, album, artist, track #, etc.). Using the default settings, iTunes keeps the iTunes Media folder organized based on how the songs currently appear in iTunes. If you change the artist name for a song from "Beatles" to "The Beatles," iTunes updates the iTunes Media folder to reflect that change for the artist-name folder.

If all of your songs are in your new iTunes library, you may need to edit song info in the iTunes window for anything that is not correct, such as what is marked as a part of a compilation (that bit of data is probably not embedded metadata). If you make a change that affects how the song file is stored, iTunes updates the iTunes Media folder accordingly.

NOTE: Some types of audio file formats do not support embedded song data. For example, I don't think WAV files support it. So those songs may end up being added to iTunes library with album and artist fields blank.