Creating a Disk from a Snapshot

When you create a disk from a snapshot, the new disk contains the same data as the snapshot. This enables you to copy data between disks within the same AZ or across AZs for purposes such as environment cloning or data backup. This section describes how to create a new data disk from a snapshot.

This section describes how to create a disk on the Snapshots page. You can also create a disk from a snapshot by specifying the Create from snapshot parameter on the disk creation page. For details, see Purchasing an EVS Disk.

Disks created from snapshots use lazy loading. They can be attached and used immediately after creation without waiting for all snapshot data to finish loading. Snapshot data is loaded into the new disk on demand in the background. Once loading is complete, the disk delivers the same performance as a newly purchased disk of the same type.

Customer impact during lazy loading:

• Impact on read/write operations

  First read (data not yet loaded): When data is accessed for the first time, the system reads it directly from snapshot storage, which results in higher latency than the disk's rated performance. Subsequent reads of the same data blocks return to normal performance.

  First write (data not yet loaded): When writing to an unloaded data block, the system must first load the corresponding snapshot data before completing the write, which may increase initial write latency. Write performance for already loaded or previously written data blocks is not affected.

  Data loading completed: The disk provides the same read/write performance as a newly purchased disk of the same type. Lazy loading does not affect the disk's final performance or capacity.

• Typical impact on workloads

  During data loading, workloads that involve large volumes of first-time random reads and writes, such as full database scans, batch file copies, or bulk data loading during application cold starts, may experience higher I/O latency and lower throughput, resulting in slower response times.

  Before loading completes, measured disk performance may fall below the IOPS and throughput limits displayed on the purchase page. Avoid running performance benchmarks during this period, as the results may not reflect steady-state performance.

  Lazy loading does not affect data integrity or correctness, and does not prevent operations such as disk attachment, partition creation, or file system mounting.

Usage recommendations:

• For performance-sensitive workloads, perform a full read after disk creation to trigger data loading before using the disk in production. For example, run dd if=/dev/vdX of=/dev/null bs=1M to sequentially read the entire disk.
• For workloads that need to go into production immediately, create disks from snapshots during off-peak hours and allow sufficient time for data loading to complete.
• Do not interpret higher read/write latency during lazy loading as a disk failure or a performance issue. If performance problems persist after loading completes, contact technical support.

• When you create a disk from a snapshot, the disk capacity must be greater than or equal to the snapshot size. If you do not specify a disk capacity, the default capacity of 10 GiB is used when the snapshot size is smaller than 10 GiB. If the snapshot size exceeds 10 GiB, the snapshot size is used as the disk capacity.

• Batch disk creation from a snapshot is not supported.
• A disk created from a snapshot has the same device type (SCSI or VBD), encryption attribute, AZ, region, and disk type as the snapshot's source disk.
• A snapshot whose name starts with autobk_snapshot_vbs_, manualbk_snapshot_vbs_, autobk_snapshot_csbs_, or manualbk_snapshot_csbs_ is automatically generated during backup. Such a snapshot can only be viewed. It cannot be used to create new disks.

1. Sign in to the console.
2. Click in the upper left corner and choose Storage > Elastic Volume Service.

   The Elastic Volume Service page is displayed.

3. In the navigation pane on the left, choose Elastic Volume Service > Snapshots.

   The Snapshots page is displayed.

4. In the snapshot list, locate the target snapshot and click Create Disk in the Operation column.
5. Configure the disk parameters. For details, see parameter descriptions and operations provided in Creating an EVS Disk.
   Note

   To specify a disk capacity larger than the snapshot size, simply enter your desired capacity in the Disk Specifications area.

6. Click Next.
7. On the confirmation page, check the disk information again.
   • If you do not need to modify the configuration, click Submit.
   • If you need to modify the configuration, click Previous.

8. Confirm the configuration and click Submit.
9. After the disk is created, view the new disk in the disk list.

   When the disk status changes to Available, the disk is successfully created.

• To buy new data disks, see Creating an EVS Disk.
• To view all the disks created from a snapshot on the snapshot details page, see Checking EVS Snapshot Details.