what does spin up mean in this sentence?

This is all incorrect. In computer science, the term originally referred to part of the process of starting a hard disk drive. HDDs have platters that spin. When a HDD starts, the platter "spins up." It is used as a metaphor when describing virtual machines that do not actually have a physical HDD or machines that contain a SSD. Source is me - a professional IT worker.

For the unbelievers, here's the definition:

Definition - What does Spin-Up mean? Spin-up is when a disk in a disk drive speeds up to the required revolutions per minute for effective writing to or reading from the disk. Conventional hard disk drives have one or more platters that revolve mechanically on a spindle while reading and writing elements alter the magnetic surface of the disk.

TechopediaPLUS

A hard disk drive (HDD), hard disk, hard drive, or fixed disk[b] is an electro-mechanical data storage device that uses magnetic storage to store and retrieve digital information using one or more rigid rapidly rotating disks [SPINNING] (platters) coated with magnetic material. The platters are paired with magnetic heads, usually arranged on a moving actuator arm, which read and write data to the platter surfaces.2 Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile storage, retaining stored data even when powered off.3[4][5]

Introduced by IBM in 1956,[6] HDDs were the dominant secondary storage device for general-purpose computers beginning in the early 1960s. HDDs maintained this position into the modern era of servers and personal computers.

hard disk drive and spinning (rotating)

And finally, in this day and age:

spin up in British English from the Collins Dictionary

VERB

(tr, adverb) computing to create (a virtual machine) using a cloud-computing service
to spin up a new server
spin up a server