This topic describes the information that you must know before you purchase ECS instances.

Resource upgrades

For information about how to upgrade the configurations of ECS instances, see Overview of instance upgrade and downgrade. Before you upgrade ECS instances, take note of the following items:
  • With the exception of ECS instances that use local storage, ECS instances allow their CPU and memory resources to be scaled and their bandwidths to be upgraded while the instances are running. You can also downgrade ECS instances based on your business needs.
  • A maximum of 16 data disks can be attached to each ECS instance. You cannot reduce the size of a data disk after it has been extended.
  • The bandwidth of each ECS instance is measured in Mbit/s and can range from 0 Mbit/s to 200 Mbit/s. You can downgrade the configurations of an ECS instance when you renew it.


The following topics describe the basic terms of ECS and how to use ECS:
  • For the terms and services related to ECS, see What is ECS?
  • For information about how to select ECS instance families, see Instance families.
  • For information about how to select images, see Select an image.
  • For the performance of Elastic Block Storage devices, see EBS performance.
  • For usage precautions on ECS instances, see Usage notes.
  • For the features of pay-as-you-go resources, see Pay-as-you-go.
  • For the features of subscription resources, see Subscription.
  • For the limits that apply to ECS, see Limits.
  • If you want to select instance types based on their benchmark data for compute performance, contact the Service Manager or submit a ticket to contact Alibaba Cloud after-sales support.