Create a snapshot-consistent group - Elastic Compute Service

You can create a snapshot-consistent group to simultaneously take snapshots for disks on one or more Elastic Compute Service (ECS) instances. When a business system spans multiple disks, you can create a snapshot-consistent group to ensure a consistent write order and crash consistency of business system data.

Background information

You can use the snapshot-consistent group feature to simultaneously create snapshots for multiple disks on one or more ECS instances. Snapshot-consistent groups are applicable to cluster services. Example scenarios that snapshot-consistent groups support:

A business system is deployed in a cluster file system that spans multiple ECS instances, and point-in-time consistency and crash-consistency are required across databases or enterprise-level applications. For example, a MySQL cluster is built on multiple ECS instances, a single Logical Volume Manager (LVM) logical volume is created across multiple volumes, or Oracle or SAP HANA clusters are migrated to the cloud.
Snapshots need to be created simultaneously for multiple nodes of a distributed application system such as a large-scale website or a multi-application collaborative system.
Disks on multiple ECS instances located in the same region need to be batch backed up and high point-in-time consistency is required.

You can use one of the following methods to create a snapshot-consistent group:

Method 1: Create a snapshot-consistent group based on a single instance
Method 2: Create a snapshot-consistent group based on multiple instances

Usage notes

Before you use the snapshot-consistent group feature, take note of the following items:

When you create a snapshot-consistent group based on an instance, take note of the following items:
- To ensure that services are not affected, we recommend that you create the snapshot-consistent group during off-peak hours.
- The instance must be in the Running or Stopped state.
- The snapshot-consistent group feature can be used to create snapshots only for enhanced SSDs (ESSDs) that are in the In Use state.
  - If the instance has ESSDs and disks of other categories attached, you can select only ESSDs on the instance to create a snapshot-consistent group.
  - ESSDs that support the multi-attach feature do not support the snapshot-consistent group feature.
- A single snapshot-consistent group can contain snapshots of up to 16 disks including the system disk and data disks and cannot exceed 32 TiB in size.
- Snapshots that you created by using the snapshot-consistent group feature are retained until they are deleted. We recommend that you delete unnecessary snapshots on a regular basis to prevent them from incurring excessive fees. For more information, see Delete a snapshot.
For the amount of time required to create a snapshot-consistent group, take note of the following items:
The amount of time required to create a snapshot-consistent group depends on the sizes of the selected disks for which to create snapshots. The first snapshot of each disk is a full snapshot and takes longer to create than subsequent snapshots. Subsequent snapshots are incremental snapshots and do not take as long to be created as the first snapshot. The amount of time required varies based on the amount of data changed since the previous snapshot. If you want to use a snapshot while it is being created, you can enable the instant access feature. For more information, see Enable or disable the instant access feature.

Billing

Snapshot-consistent groups are free of charge but snapshots contained in snapshot-consistent groups are billed based on the amount of storage space the snapshots consume. After the instant access feature is enabled, you must pay both snapshot storage fees and instant access feature fees. For more information, see Snapshots.

Method 1: Create a snapshot-consistent group based on a single instance

Log on to the ECS console.
In the left-side navigation pane, choose Instances & Images > Instances.
In the top navigation bar, select a region.
Find the instance based on which you want to create a snapshot-consistent group and choose More > Disk and Image > Create Snapshot-consistent Group in the Actions column.

In the Create Snapshot-consistent Group dialog box, configure the parameters described in the following table.


Parameter		Description
Select cloud disk		Select the enhanced SSDs (ESSDs) for which you want to create snapshots.
Snapshot parameter settings	Snapshot-consistent Group Name	Enter a name for the snapshot-consistent group for easy management.
	Description	Enter a description for the snapshot-consistent group for easy management.
	Tag	Add tag key-value pairs to the snapshot-consistent group for easy management.
	Snapshot speed available	Enable Instant Access: You can select this check box to enable the instant access feature. By default, this feature is disabled. Note The instant access feature supports only ESSDs. For more information, see Enable or disable the instant access feature. Snapshot Speed Available Duration: After you enable the instant access feature, you can specify a validity duration for the feature. The default validity duration is one day. The instant access feature is automatically disabled when the specified duration ends.
	Application-consistent Snapshot	Enable Application-consistent Snapshot: You can select this check box to enable the application-consistent snapshot feature. By default, this feature is disabled. For more information about how to enable the application-consistent snapshot feature, see Create application-consistent snapshots in the ECS console. Note The application-consistent snapshot feature is available in the China (Hong Kong), Singapore (Singapore), China (Hangzhou), China (Shanghai), and China (Beijing) regions.

Click OK.
After the snapshot-consistent group is created, you can choose Storage & Snapshots > Snapshots and click the Snapshot-consistent Group tab to view the snapshot-consistent group.

Method 2: Create a snapshot-consistent group based on multiple instances

Note The application-consistent snapshot feature can be used to create snapshots based only on a single instance at a time. For information about how to use the application-consistent snapshot feature, see Method 1: Create a snapshot-consistent group based on a single instance.

Log on to the ECS console.
In the left-side navigation pane, choose Storage & Snapshots > Snapshots.
In the top navigation bar, select a region.
To create a snapshot-consistent group based on multiple instances, you must select the region in which the instances are located. For example, if you want to create a snapshot-consistent group based on your instances deployed in the China (Hohhot) region, you must select China (Hohhot) from the drop-down list.
Click the Snapshot-consistent Groups tab. Then, click Create Snapshot-consistent Group.

On the Create Snapshot-consistent Group page, configure the parameters described in the following table.


Parameter		Description
Data Source		Select the instances based on which you want to create the snapshot-consistent group. Instances can be searched only by instance ID. You can select one or more instances.
Select cloud disk		Select the ESSDs for which you want to create snapshots. Take note of the following items: Only ESSDs can be selected. Up to 16 disks can be selected, including the system disk and data disks. The total size of the selected disks cannot exceed 32 TiB.
Snapshot parameter settings	Snapshot-consistent Group Name	Enter a name for the snapshot-consistent group for easy management.
	Description	Enter a description for the snapshot-consistent group for easy management.
	Tag	Add tag key-value pairs to the snapshot-consistent group for easy management.
	Snapshot speed available	Enable Instant Access: You can select this check box to enable the instant access feature. By default, this feature is disabled. Note The instant access feature supports only ESSDs. For more information, see Enable or disable the instant access feature. Snapshot Speed Available Duration: After you enable the instant access feature, you can specify a validity duration for the feature. The default validity duration is one day. The instant access feature is automatically disabled when the specified duration ends.

What to do next

After a snapshot-consistent group is created, you can perform the following operations:

Use the snapshot-consistent group to roll back disks. For more information, see Roll back disks by using a snapshot-consistent group.
Access the snapshot-consistent group and create a custom image from a snapshot contained in the group. For more information, see Create a custom image from a snapshot.