Disks are block-level data storage products provided by Alibaba Cloud for ECS. They feature low latency and high performance, durability, and reliability. Disks use a distributed triplicate mechanism to ensure 99.9999999% data reliability for ECS instances. If service disruptions occur (for example, due to hardware failure) within a zone, data in that zone is copied to an unaffected disk in another zone to help ensure data availability.
As with hard disks, you can partition and format cloud disks that are attached to ECS instances, create file systems and persistently store data on the cloud disks. The following table lists the disk categories by performance.
|Enhanced SSD (ESSD)||ESSDs are based on the next-generation distributed block storage architecture and the 25 Gigabit Ethernet (25GE) and remote direct memory access (RDMA) technologies. Each ESSD can deliver up to one million random IOPS and has low latency. For more information, see Enhanced SSDs.|
|Standard SSD||Standard SSDs are high-performance disks that feature consistent and high random IOPS performance and high data reliability.|
|Ultra disk||Ultra disks feature high cost-effectiveness, medium random IOPS performance, and high data reliability.|
|Basic disk||Basic disks feature high data reliability and standard random IOPS performance.|
A disk can be used as a system disk or a data disk based on the type of the stored data and the creation method of the disk.
|Type||Description||Can be created separately||Maximum number of disks per instance||Disk size|
|System disk||Shared access to a system disk is not allowed. When a system disk is initialized, the image determines the operating system type and application data. Only cloud disks can be used as system disks.||No. A system disk must be created with an instance and shares the same lifecycle as the instance.||1||The minimum size of a system disk depends on the image. The actual size is displayed
on the instance buy page.
|Data disk||A data disk is used to store application data. It can be created separately or together with an ECS instance. Cloud disks or block storage devices of other types such as local disks can be used as data disks. For more information, see Local disks.||Yes.||16||Up to 32 TiB. For more information, see Block Storage performance.|
A disk can be attached to only one ECS instance that is in the same zone as the disk.
For more information, see the "Block Storage limits" section in Limits.
- Disks that are created with subscription instances or created separately for subscription instances are billed on a subscription basis.
- Disks that are created with pay-as-you-go instances or created separately for pay-as-you-go instances are billed on a pay-as-you-go basis. Storage capacity units (SCUs) can be used to offset the bills of pay-as-you-go disks.
After a disk is created, you can change its billing method as needed. For more information, see Convert the billing method of a cloud disk.
You can perform the following operations on a disk as needed:
|Attach an idle pay-as-you-go disk to an ECS instance|
|Create a subscription data disk||Create a subscription disk|
|Create a data disk separately|
|Encrypt the data stored on a disk||Encryption overview|
|Resize a system disk||Overview|
|Resize a data disk||Overview|
|Replace the system disk||Replace the system disk (public images)|
|Back up disk data|
|Copy the operating system and application data of an ECS instance||Create a custom image from a snapshot|
|Restore a disk to its initial status||Reinitialize a system disk|
|Restore a disk to its status at a specific point in time||Roll back a disk|
|Release an idle subscription disk|
|Release an idle pay-as-you-go disk|