Core storage

Core Storage is a logical volume management system on macOS that was introduced by Apple to Mac OS X Lion. Core Storage is a layer between the disk partition and the file system.

Core Storage is the basis for Apple's Fusion Drive technology, which presents several partitions on multiple drives as a single logical volume. It does this by using tiered storage, whereby it keeps the most frequently used blocks on the fastest storage device in the pool, which is by default, an SSD.

Apple CoreStorage defines four types of objects, instances of which are uniquely represented by a UUID:

Apple's current implementation is not intended for the traditional roles that LVMs were/are used for. For example, as of 2014, the pool cannot be expanded as the storage grows. Also in 10.7, the pool can comprise only a single drive. Core Storage also doesn't support thin provisioning, different RAID levels or resiliency. However, like in Linux, but unlike in Windows, the LVM can be used as the root filesystem, a significant advantage for home users who prefer to have a single volume for the OS and storage or find the need to extend the amount of storage available to the core operating system.

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