The decision of blade server vs. rack server, the most common type of server, is an important one. To make the right choice, you’ll need to pay attention to the pros and cons of each and how they complement or challenge your needs.
Many vendors offer both types of servers through different series and models. So, choosing one can be understandably difficult.
In this article, we will provide the following:
| Features | Blade Server | Rack Server |
| Definition | Architecture with multiple servers in a single Chassis | Rack-mounted dedicated servers |
| Power | Less | More |
| Maintenance | Less | More |
| Cost | Less | More |
| Size | Small and compact | Large |
| Cabling | Less | More |
| Business model | Big organizations | Small business |
| Design | Modular | Stand alone |
| Mount inside | Chassis | Special rack |
| Operational cost | Low | High |
| PCIe slots | No support for PCIe slots | Support for up to 2 PCIe 2.0 slots |
| Optical drive | No support for an optical drive | Optional front panel optical drive for CD and DVD media |
| Cisco servers | Managed from the UCS Fabric Interconnect by Cisco UCS Manager | Features Cisco Integrated Management Controller (CIMC) and can be managed independently or from Cisco UCS Manager if connected to a UCS Fabric Interconnect |
| Examples - Cisco | UCS B200M4; UCS B420M4 | UCS C220 M4 |
| Example - HP | HP BL460c Gen9; HP BL660c Gen9 | HP DL360 Gen9; HP DL160 Gen9 |
| Example - Dell | Dell M630; Dell M830 | Dell R630 |
| Example - Lenovo | Lenovo x240M5; Lenovo Flex System x440 | Lenovo x3550 M5 |
A blade server is a small, modular server housed in server bays. Besides the CPU, memory, and network controllers, these servers may also have storage built-in. However, any other components the server needs must be housed in the server chassis where all the blade servers go.
In other words, blade servers share power and other resources via the server chassis. This allows them to be smaller in size. A blade server bay or rack can house more units efficiently — for instance, a blade server bay can hold up to 20 servers. The bay can even be mounted onto a rack, allowing for more density.
A rack or rack-mounted server is a server made to be mounted on a rack. A server rack is an enclosure that houses servers and other equipment (for example, storage). As a result, these servers have standard dimensions so they can fit into the rack.
Rack servers can be stacked easily, allowing a rack to house multiple servers, typically up to 10. The rack is configured with peripherals to control and manage the individual servers. Although smaller than traditional tower servers, these servers can have more internal components, including graphics, video cards, and power supplies.
Rack servers are commonly used in data centers because of the standard dimensions, smaller footprint, and installation convenience.
Here are the main differences between rack and blade servers that ultimately contribute to their feasibility for different use cases.
The primary difference between blade and rack servers is their design. Blade servers are modular and designed with a circuit board that shares multiple components like CPU, memory, storage, et cetera.
On the other hand, rack servers have a bigger form factor as they have more architecture components. They are standalone servers that can run independently, unlike blade servers that take power from the chassis.
Although rack and blade servers offer higher density than tower servers, blade servers are best for high-density data centers. Their design allows for more units to be housed in a smaller space.
Rack servers are also dense by design, as you can mount multiple in a single rack. However, unlike blade servers, they don’t offer the same level of density, which means they require more space than blade servers.
In blade servers, the chassis is fitted with power supply components, so all the servers share the power supply in the server bay. While this design saves cost, it also impacts reliability because if the power supply fails, all servers housed in the chassis will be affected.
In the case of rack servers, the power supply may be shared or made redundant for each server. In the latter case, the reliability is higher, as failure in the power supply for one unit doesn’t necessarily impact other units in the rack.
Compared with blade servers, rack servers have a higher power draw.
Because of their high-density design, blade and rack servers can produce a lot of heat. So, both of these server types require constant cooling and temperature management.
Cooling rack servers are relatively easier as they have built-in fans. Also, other cooling components can be configured in the rack itself.
Regarding customizability, blade servers are comparatively easier to customize. So for enterprises looking to customize the design and components of their servers, blade architecture is the better choice. As a result, these servers can be customized to handle specific workloads, for example, compute-intense AI workloads.
Rack servers can also be customized, but not to the degree and convenience of blade server bays.
Blade servers are modular, so they’re hot-swappable. This means a server can be removed and replaced from a cluster without powering down the other servers in the chassis. So, should a component or entire server fail, it can be removed from the bay easily.
Rack servers are easy to maintain but may induce some downtime, depending on the configuration of the rack. Moreover, racks can be large and house different appliances, complicating the replacement efforts.
The price of a server depends on a variety of factors. Generally speaking, rack servers are cheaper. Blade servers require a dedicated chassis, which adds to the production cost. However, they can be cost-effective because of their high density.
Both blade and rack servers call for cooling infrastructure. The former does require more cooling provisions, so that should also be factored into the operational expenses of these servers.
Here are the advantages of blade servers summarized:
Here are the advantages of rack-mounted servers:
In data centers, rack servers have been ubiquitous because of their configuration and ease of scalability. However, blade servers are gradually gaining momentum in the data center space because of their high computing power.
Blade servers are a suitable choice for large processing clusters, the kind needed for handling complex workloads. Enterprises that require more processing from their servers should lean toward blade clusters. The customizability, of course, is an added advantage.
Remember that they produce a lot of heat, so they require dedicated cooling solutions that prevent equipment damage.
Blade servers are also a good option if you’re pressed for floor/rack space.
For traditional data centers that handle data storage primarily, rack servers are the undisputed choice. They’re cheaper, last many years, and can be maintained easily.
Rack servers are also good for smaller deployments, for example, server rooms in branch offices. They can be configured according to your needs rather easily.
The differences are plentiful when making the choice between a blade server vs. a rack server. You should choose the kind that meets your business and technical needs, but no matter what type of server you choose, you must do your homework before settling on a brand and model.
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