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Notes and Constraints

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This section describes the constraints on using EVS.

Specifications

Table 1 Specifications

Resource Type

Item

Description

Disk performance

Major disk performance metrics include IOPS, throughput, and latency.

Different types of EVS disks have different performance. For details, see Disk Types and Performance.

Security

Table 2 Security

Item

Description

Disk encryption

  • The encryption attribute of a disk cannot be changed after the disk is created.
  • If you use an encrypted disk to create a backup, the backup generated will be an encrypted backup. You cannot modify the encryption attribute of the backup.
  • If you use an encrypted disk to create an image, the image generated will be an encrypted image. You cannot modify the encryption attribute of the image.
  • If you use an encrypted disk to create a snapshot, the snapshot generated will be an encrypted snapshot. You cannot modify the encryption attribute of the snapshot.
  • If you use an image that does not support lazyloading to create a disk, the disk created will be an encrypted disk. You cannot modify the encryption of the disk.

Quotas

Table 3 Quotas

Resource Type

Default Quota

Tags

10

Disks

Default quotas vary depending on regions. See the quotas shown on the console.

Disk capacity (GB)

Snapshots

Operations

Table 4 Operations

Scenario

Item

Description

Disk creation

Maximum number of disks that can be created at a time

100

Disk creation

Disk creation from snapshot

For details, see the constraints in Creating a Disk from a Snapshot.

Disk creation

Disk creation from backup

  • Batch creation is not supported. One can create only one disk from a backup at a time.
  • One backup cannot be used for concurrent disk creation operations at the same time. For example, if you are creating disk A from a backup, this backup can only be used to create another disk after disk A has been created.
  • If a disk is created from a backup of a system disk, the new disk can be used as a data disk only.

Disk creation

Disk creation from image

  • The device type of the new disk is the same as that of the image's source disk.
  • The encryption attribute of the new disk is the same as that of the image's source disk.

Disk creation

Device type

The device type of a disk cannot be changed after the disk is created.

Disk creation

Disk sharing

The sharing attribute of a disk cannot be changed after the disk is created.

Disk creation

Disk encryption

The encryption attribute of a disk cannot be changed after the disk is created.

Disk attachment

Constraints on region and AZ

The disk and the server must be in the same region and AZ.

Maximum number of servers that a non-shared disk can be attached to

1

Maximum number of servers that a shared disk can be attached to

16

Maximum number of disks that can be attached to an ECS

This number varies depending on the ECS type.

For details, see section "Can I Attach Multiple Disks to an ECS?" in the Elastic Cloud Server User Guide.

Device name

  • System disk: /dev/vda, /dev/sda, and /dev/xvda
  • Data disk: /dev/vd[b-z], /dev/sd[b-z], and /dev/xvd[b-z]

Disk capacity expansion

Capacity expansion

Disk capacity can be expanded, but cannot be reduced.

Capacity expansion of non-shared disks

Some server OSs support the capacity expansion of non-shared, In-use disks.

For details, see .

Capacity expansion of shared disks

A shared disk must be detached from all its servers before expansion. This means that the shared disk status must be Available.

Expansion increment

1 GiB

Disk detachment

System disk detachment

A system disk can only be detached offline, which means that the server must be in the Stopped state.

Data disk detachment

A data disk can be detached online or offline, meaning that its server can either be in the Running or Stopped state.

Disk deletion

Deletion of disks

  • The disk status is Available, Error, Expansion failed, Restoration failed, or Rollback failed.
  • The disk is not locked by any service.
  • The shared disk has been detached from all its servers.

Snapshot creation

/

For details, see the constraints in Creating an EVS Snapshot.

Snapshot data rollback to disks

/

  • Snapshot data can only be rolled back to source EVS disks. Rollback to a different disk is not possible.
  • If the snapshot status is Creating, it cannot be used to roll back disk data.
  • 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 roll back the disk data.

Snapshot deletion

/

For details, see the constraints in Deleting an EVS Snapshot.

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