The HP Zbook 17 G2 has a better storage medium than most portable PCs of this spec and age. This laptop has an SSD storage medium, whereas most portable PCs that have been around for around the same time as it have an HDD storage medium. Solid State Drives (SSD) store data in semiconductors on a circuit board rather than using magnetic or optical media. Solid State Drives have no moving parts which makes them very fast and reliable.
This notebook PC's storage medium (SSD) is actually the best storage medium across all many processor core laptops that have been available for a comparable time to the Zbook 17 G2.
The worst storage medium amongst similar types of notebook PC is HDD.