Server Farm is the most common term, I think. Data Center is another term, but I think that may be a specific type of Server Farm.
A collection. A library.
A large group of trees is an orchard, a woods, a forest, or a jungle. A collection of trees of different types is called an Arboretum
A large collection of foreign colonies is called an empire. Empires are formed when one country or group of people control various territories and peoples outside their own borders.
The 1U Rackmount set of servers are designed to process and transfer large amounts of data as fast as possible. They are called rackmount servers as they allow you to stack multiple on top of each other often in a series of racks.
Ashurbanipal had a large collection of books.
Mainframes are large centralized computers found in sizable enterprises.
A server merely provides a service when asked. Severs can provide different kinds of services. Large networks typically have many servers. Each server is usually dedicated to providing a single service. Those that provide file-sharing facilities are called file servers. Those that server Web pages are called Web servers.
Characteristics of the powerful servers is that they should be able to handle a large number of clients at once.
At collection of stamps is refered to as a stamp collection. They are frequently kept in albums. Philately is the name for the study and collection of stamps.
The complete subject of the sentence is "a large collection of music manuscript." It includes the article "a" along with the descriptive phrase "of music manuscript," which specifies the type of collection.
it is called a range of mountains
a collection of fish is called a school of fish