When hosting servers or renting server racks, you sometimes hear terms like 1U, 2U, 4U, or 42U. What do these terms mean?
I. Units related to "U"
U is a unit used to represent the external dimensions of a server; it's an abbreviation for "unit." It defines the server's dimensions, allowing it to be placed in a rack at a specific size. The rack has screw holes for mounting servers, ensuring the aligning screws on the rack allow for easy installation of each server within the required space.
II. 1U Server, 2U Server, 4U Server
The server's dimensions are defined as width (48.26cm = 19 inches) and height (multiples of 4.445cm), with the thickness (height) in units of 4.445cm.
Among rack-mount server sizes, the most common are 1U, 2U, and 4U servers. Their dimensions are: 1U = 4.445 cm, 2U = 4.445 * 2 = 8.89 cm, and 4U = 4.445 * 4 = 17.78 cm. In practical use, 1U or 2U servers are the most frequently used. Because service providers calculate fees based on server space usage, using a 1U server is the most space-efficient and cost-effective option. However, the scalability of a 1U server is not as good as that of a 2U server. A 1U server can accommodate a maximum of 4 hard drives, while a 2U server can accommodate 8. The number of PCI slots also differs: 1U has a maximum of 2, while 2U can have up to 6.
III. 42U Server Rack
42U server racks are generally classified as follows:
1) By width: 42U racks are available in 600mm and 800mm widths, and depths include: 600mm, 800mm, 900mm, 960mm, 1000mm, 1100mm, 1200mm, etc.
2) Based on actual needs: In addition to the actual usable size of 42U, the width and depth can be customized according to actual needs.
A server rack has a limited capacity; a 42U rack height doesn't necessarily mean it can hold 42 1U servers. After installing the servers, space needs to be allocated for cooling and movement, cable management, and other equipment like switches, firewalls, and monitors. Therefore, the number of servers a 42U rack can hold depends on the specific equipment. So, the question is, how many server units are typically deployed in a single rack?
The number of servers that can be deployed in a server rack depends on many parameters, such as the physical parameters of the servers (size, power consumption, heat generation), as well as the rack's power supply, cooling, and load-bearing capacity. To determine the maximum number of servers that can be deployed, consider the following key parameters:
1) Reservation: 1U space is reserved between each device for heat dissipation, and space is reserved for switches, with PDU placement also considered;
2) Generally, a redundant 10KW power supply is provided, with a static load capacity of not less than 1200kg (determined based on the computer room construction parameters).
3) Without exceeding power limits, the total number of device units (U) in a single rack should generally not exceed 26U.
In a server rack, the number of all-1U devices deployed is generally no more than 16, all-2U devices are generally no more than 12, and all-4U devices are generally 4 to 7.
