El Capitan has made the checking and repair of storage more complex. Here is a clear explanation of what to do.
disk
Being a hybrid, naming disks and volumes can get complex in OS X. This article demystifies them.
228.7 GB of my internal disk is occupied by ‘Other’. Where has this gone, and how can I reclaim it?
My hard disk is running out of space, and only has 104 GB left of its original 500. How come?
How can I get an audio CD out of the optical drive of my MacBook?
When I run Disk Utility on my iMac (OS X 10.6.8), it keeps reporting invalid volume/directory counts. How can I stop it?
Most of the computer-like devices that you use now store their data on solid-state disk (SSD) rather than traditional hard disk (HD) components. Are they also the best way ahead for regular computers?
The Eclectic Light Company 