Yosemite’s Switch to Core Storage
Craig Cohen (via Clark Goble):
Yosemite uses a volume format known as Core Storage. It is the enabling technology behind Fusion Drive and FileVault.
Core Storage is a reliable, high-performance volume format. It provides increased crash protection, ditto blocks for metadata, copy-on-write B-tree catalogs, in-place transformations for backgrounding the disk encryption used by FileVault, and intelligent block-level data migration used by Fusion Drive.
Yosemite will auto-convert your drive so long as your Mac has hardware support for encryption. HFS+ is still there; it’s just wrapped in another layer.
