Snapshot prefetch (Public Preview)

Retention period

The retention period is the duration (in hours) that the prefetch feature stays active and keeps resources reserved. It cannot exceed the snapshot's own retention period. After you enable prefetch, the system prefetches data in the background and reserves the corresponding resource quota. The effective duration of prefetch is determined by the retention period, and you can manually disable it at any time.

• While active: Prefetch performance advantages are possible only for disks created from this snapshot during this period.   

• After expiration: Prefetch is automatically invalidated, and disks created from this snapshot must load data from OSS without any performance advantage.

Number of concurrent disk creations

The number of concurrent created disks determines the maximum number of disks per batch request that can receive prefetch benefits. It consists of two components: the pre-configured number of concurrent created disks and the available number of concurrent created disks. The system allocates backend resources based on this value to ensure performance-preserved data loading at the specified scale.

• Pre-configured number of concurrent created disks: The maximum number of disks per batch that can receive performance advantages, as configured when enabling snapshot prefetch. This value defines the guaranteed performance scale. Disks created within this quota have performance-preserved data loading; disks created beyond this quota do not receive prefetch benefits.

• Available number of concurrent created disks: The remaining quota currently available for creating disks with prefetch advantages.

  • Quota consumption: Prefetch capacity is a consumable resource. Each time a performance-enhanced disk is created, it consumes one unit of the available number of concurrent created disks.

  • Quota recovery: Consumed quota automatically recovers up to the pre-configured number of concurrent created disks. Recovery speed depends on the full snapshot size - larger snapshots recover more slowly.

Billing formula

The total snapshot prefetch cost for a single region is the sum of fees generated by all prefetch-enabled snapshots across all availability zones in that region. The formula for a single availability zone is:

Prefetch fee = Snapshot capacity * Duration * Number of concurrent created disks * Snapshot prefetch unit price

Billing lifecycle

• Billing starts: When the snapshot prefetch status changes to Enabled.

• Billing stops: Snapshot prefetch billing stops automatically when any of the following occurs.

  • You manually disable the prefetch feature for the snapshot.

  • The prefetch retention period expires and the feature is automatically disabled.

  • Your account is overdue and the prefetch feature is automatically disabled.

    After you pay the overdue balance, the feature remains disabled and does not resume automatically. To continue using it, you must manually re-enable it.

Add snapshot prefetch

1. Go to the ECS console - Snapshots page. In the upper-left corner, select the resource group and region where your resources are located.

2. On the Disk Snapshots tab, find the target snapshot. In the Actions column, click the icon and select Manage Snapshot Prefetch.

3. On the Snapshot Prefetch page, click New Zone.

4. On the New Zone page, configure the prefetch parameters. Read and agree to the terms of service, then click Confirm.

   Parameter	Description
   Zone	Select the availability zone for prefetch. The prefetch capability applies only to the specified snapshot in the specified availability zone.
   Retention Period	The duration that the prefetch capability stays active and retains quota, in hours. This value cannot exceed the snapshot's own retention period.
   Number of concurrent created disks	The number of disks per batch that can receive prefetch performance advantages while the retention period is active. Valid values: 100 to 10,000. Must be a multiple of 100.   Important Disks created within this quota have performance-preserved data loading, while disks created beyond it do not receive prefetch benefits.

5. Confirm the prefetch status.

   After configuration, the prefetch status changes to Prefetching. When prefetching completes, the status changes to Enabled and the retention timer starts. The displayed available count is the current number of disks that can be created with performance advantages.

   Prefetch completion time depends on the snapshot size - larger snapshots take longer.

Manage existing prefetch configuration

1. Go to the ECS console - Snapshots page. In the upper-left corner, select the resource group and region where your resources are located.

2. On the Disk Snapshot tab, find the target snapshot. In the Actions column, click the icon and select Manage Snapshot Prefetch.

3. On the Snapshot Prefetch page, find the target prefetch availability zone.

   • Modify a configuration: Click Modify in the Actions column.

     • Modify retention period: Takes effect immediately, but the calculation is based on the original prefetch start time, not the current modification time. The new prefetch end time must be later than the current time.

     • Increase number of concurrent created disks: The change takes effect after the available number of concurrent created disks reaches the new pre-configured level. During the transition period (which depends on the increase amount and snapshot size), billing continues at the old configuration.

     • Decrease number of concurrent created disks: The change requires time to take effect (depending on the decrease amount and snapshot size), during which billing continues at the old configuration. After the change takes effect, billing continues at the new configuration.

   • Disable: Click Disable in the Actions column. The prefetch status changes to Disabled and billing stops.

     Important

     After disabling, the prefetch data for this availability zone becomes unavailable. Subsequent disk creation will not benefit from prefetch performance. Proceed with caution.

   • Enable: Click Enable in the Actions column. The prefetch status changes to Prefetching. When prefetching completes, the status changes to Enabled and billing starts.

How do I create a disk with prefetch performance advantages?

1. Before you begin, ensure all of the following conditions are met:

   • The snapshot's prefetch status is Enabled.

   • The target cloud disk is an ESSD or ESSD AutoPL disk and does not belong to a dedicated block storage cluster.

   • The number of disks created in a single request does not exceed the current available number of concurrent created disks.

   • You create an unencrypted disk from an unencrypted prefetched snapshot, or you create a disk from an encrypted prefetched snapshot without changing the encryption key.

2. Use the snapshot to create a data disk in a prefetched availability zone.

3. After the disk is created, go to the ECS console - Block Storage - Disks page.

4. Find the new cloud disk. Hover over the icon in its Tags column. If the Tag Key is acs:ecs:disk:performancePreserved and the corresponding Value is true, the disk was successfully created with prefetch performance advantages.

Displaying the Full Snapshot Size column

1. On the ECS console - Snapshots page, click the icon.

2. In the Columns Hidden list, move Full Snapshot size to the list of Columns Displayed and then click OK. You can now view the full snapshot size for your target snapshot.

Checking the prefetch status

1. Go to the ECS console - Snapshots page.

2. Locate the snapshot and verify using any of the following methods:   

   • Hover over the icon in its Tags column. If the Tag Key is acs:ecs:snapshot:feature:warmupand the corresponding Value is enable, prefetch is enabled for the snapshot.

   • Attribute column: Shows Prefetched for snapshots with prefetch enabled.