Constraints

Capacity of a data disk

• High I/O: 10 GiB to 32,768 GiB
• General Purpose SSD: 10 GiB to 32,768 GiB
• Ultra-high I/O: 10 GiB to 32,768 GiB
• Extreme SSD: 10 GiB to 32,768 GiB

Disk performance

High I/O

• Maximum IOPS per disk: 5,000
• Maximum throughput per disk: 150 MiB/s

Ultra-high I/O

• Maximum IOPS per disk:
• Maximum throughput per disk: 350 MiB/s

General Purpose SSD

• Maximum IOPS per disk: 20,000
• Maximum throughput per disk: 250 MiB/s

Disk creation restrictions on accounts

Permission requirement

The account used to create EVS disks must have the evs:volumes:create permission. For how to add permissions, see EVS Custom Policies

Disk creation

Maximum number of disks that can be created at a time

100

Disk creation from snapshot

• The disk type of the new disk is the same as that of the snapshot's source disk.
• The device type of the new disk is the same as that of the snapshot's source disk.
• The encryption attribute of the new disk is the same as that of the snapshot's source disk.
• Batch creation is not supported. One can create only one disk from a snapshot at a time.

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 be used to create another disk only 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 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.

Device type

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

Disk sharing

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

Disk encryption

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

Disk attachment

Constraints on region and AZ

The disk and 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 value varies with ECS types.

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

Maximum number of disks that can be attached to a BMS

60 (1 system disk and 59 data disks)

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 Expanding Capacity for an In-use EVS Disk.

Capacity expansion of shared disks

A shared disk must be detached from all its servers before expansion. That is, 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, that is, 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

Maximum number of snapshots that can be created for a disk

7

Snapshot data rollback to disk

• A snapshot can be rolled back only to its source disk. Rollback to another disk is not possible.
• A snapshot can be rolled back only when the snapshot status is Available and its source disk status is Available (not attached to any server) or Rollback failed. If the source disk is attached, detach the disk first.
• 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.
• If you first roll back the snapshot to the original disk, you cannot use the snapshot to create a new disk then.

Tag

Maximum number of tags that can be added for a disk

10