I keep my library on an external hard drive 4TB. It's full. Can I use more than one hard drive to keep my library on?

Hi dancutler

As far as I understand it you can not run itunes accross mulltiple hard drives.

You can however create a software RAID to combine your multiple drive's into a drive location that itunes can use.

This is what I have done.

maybe others will have better solutions.

Cheers

Tony

Yes, of course.

Create a concatenated disk set

Increase storage space with a concatenated RAID set (also called “Just a Bunch of Disks” or JBOD). If you need one large disk, but you have only several smaller disks, you can create a concatenated disk set to use several small disks as one large disk.

1. Open Disk Utility, in the Utilities folder in Launchpad.

2. Select one of the disks that you want in the set, and then click RAID.

3. Click Add (+), and type a name for the RAID set.

4. Choose a format from the Format pop-up menu. Usually you’ll choose the Mac OS Extended (Journaled) format.

5. Choose Concatenated Disk Set from the RAID Type pop-up menu.

6. Drag the disks you want to add to the set to the list on the right.

7. Click Create.

Exerpt from:

Disk Utility 12.x: Create a RAID set - Apple - Support

Note that the biggest CON to concatenated RAID configurations is vulnerability to volume failure. If either disk fails, the whole volume fails. If you choose this option, I would highly recommend backing up your music to a cloud service. There are very cheap per GB/storage, and some of the most reputable actually offer unlimited storage:

Five Best Cloud Storage Providers - Lifehacker

This will require the OP to erase the original 4TB disk which they may not want to do.

This is a very valuable point that I failed to mention. Thank you, Michael. You will want to back up your data to another drive, or the cloud storage mentioned, beforehand, as creating the 8 TB JBOD requires erasing and reformatting the 2 x 4 TB drives, one of which contains all your data.