This topic describes general-purpose and dedicated-disk instance categories of ApsaraDB for MongoDB.
Categories
Category | Description | Scenario |
General-purpose | General-purpose instances on the same physical server occupy dedicated memory and storage but share CPU and I/O resources. As such, the instances may compete for resources. CPU resources are highly reused among shared instances that are deployed on the same physical server. This maximizes cost-effectiveness.
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Dedicated-disk | Dedicated local-disk instances on the same physical server occupy dedicated memory, storage, and CPU resources, but share I/O resources. As such, the instances may compete for I/O resources. Dedicated cloud-disk instances on the same physical server occupy dedicated memory, storage, and CPU and I/O resources. As such, the instances do not compete for resources. Dedicated cloud-disk instances also provide higher performance stability and are less affected by other instances that are deployed on the same physical server than dedicated local-disk instances. Dedicated-host instances occupy all resources of a host and do not compete for resources.
| Business scenarios where databases are used as core systems. The scenarios include providing finance, e-commerce, and large and medium-sized Internet services and handling government affairs. |
The following figure shows the differences between general-purpose instances, dedicated local-disk instances, and dedicated cloud-disk instances. 
Instance specifications
For more information about instance specifications such as the number of vCPUs, memory, storage capacity, maximum number of connections, and IOPS, see Overview.
Pricing
For more information about the pricing of each instance type, see Billable items.
Change instance specifications
You can change the specifications of an instance. For more information about specific operations, see Overview.