Constraints

This section describes the constraints on using EVS.

Table 1 Constraints on using EVS

Scenario	Item	Restrictions
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	Common I/O	Maximum IOPS per disk: 1,000 Maximum throughput per disk: 90 MiB/s
	High I/O	Maximum IOPS per disk: 3,000 Maximum throughput per disk: 150 MiB/s
	General Purpose SSD	Maximum IOPS per disk: 20,000 Maximum throughput per disk: 250 MiB/s
	Ultra-high I/O	Maximum IOPS per disk: 20,000 Maximum throughput per disk: 350 MiB/s
	Extreme SSD	Maximum IOPS per disk: 128,000 Maximum throughput per disk: 1,000 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	Data of a snapshot can be rolled back only to its source disk. Rollback to another disk is not possible. Data of 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. Spot instances do not support snapshot-based rollback of the disk data.
Tag	Maximum number of tags that can be added for a disk	10

last updated: 2024-11-13 14:31 UTC - commit: 8d943812e7d8424718eb8315e2294eccf373143f