Function Overview

EVS APIs are classified as follows:

• APIs for EVS with customized specifications (EVS APIs)
• Native OpenStack APIs that comply with OpenStack community specifications (OpenStack APIs)
  The two types of APIs offer similar functions but apply to different application scenarios. You can use OpenStack APIs to interconnect EVSs with open-source ecosystem tools. EVS APIs have enhanced certain functions based on the OpenStack APIs. It is recommended that you use EVS APIs.

With the EVS SDKs, you can easily invoke EVS APIs to create Internet-based applications on HUAWEI CLOUD.
Currently, SDKs support Java, Python, and Go languages. You can use APIs or any other well-known SDKs.

EVS disk types are classified into ultra-high I/O, general purpose SSD, high I/O, and common I/O based on the disk I/O performance. 
EVS disk types differ in performance and the main performance metrics include: IOPS, throughput and read/write I/O latency.

EVS device types are classified as Virtual Block Device (VBD) and Small Computer System Interface (SCSI) based on whether advanced SCSI commands are supported.

• VBD is the default EVS disk device type. VBD EVS disks support only basic read/write SCSI commands.
• SCSI EVS disks support transparent SCSI command transmission and allow the server OS to directly access the underlying storage media. 

After you attach an EVS disk to a server, you need to initialize the disk to use it.

• System Disk: System disks are automatically created and initialized during the server creation. The default disk partition style is master boot record (MBR).
• Data Disk: If a data disk is created along with a server, it will be automatically attached to the server; If a data disk is created separately, you need to manually attach it to a server.
  In both cases, you must initialize the data disk before using it.

If the capacity of an existing disk is insufficient, you can expand the disk capacity.
Both system disks and data disks can be expanded. A system disk can be expanded up to 1 TB, and a data disk to 32 TB. Currently, disk capacities can be expanded only.
A capacity expansion operation includes the following steps:
1. Expand the disk capacity on the management console.
2. Log in to the server and extend the disk partition and file system.

Shared EVS disks are block storage devices that support concurrent read/write operations and can be attached to multiple servers. Shared EVS disks feature multiple attachments, high-concurrency, high-performance, and high-reliability. They are usually used for enterprise key applications that require cluster deployment and high availability.
A shared EVS disk can be attached to a maximum of 16 servers. You must deploy a shared file system or a cluster management system, such as Windows MSCS, Veritas VCS or CFS, to implement file sharing.
Notice: To use shared EVS disks, you must set up a shared file system or similar cluster management system. If you directly attach EVS disks to multiple servers, the EVS disks cannot be shared and data may be overwritten.

The disk backup function provided by Cloud Backup and Recovery (CBR) allows you to create backups for your EVS disks. During the backup, you do not need to stop the server.
If data loss or data damage occurred due to virus invasions, misoperations, or software and hardware faults, you can use backups to restore the data, guaranteeing your data correctness and security.
You can use backups to restore EVS disks to the specified backup time points. In addition, you can use backups to create an EVS disk so that the EVS disk contains the backup data in its initial state.

As a major disaster recovery (DR) approach, an EVS snapshot is a complete copy or image of the disk data at a specific time point.
You can create snapshots to rapidly save the disk data at specified time points. If data is lost, the snapshot can be used to restore the data to point in time. In addition, you can use backups to create an EVS disk so that the EVS disk contains the backup data in its initial state.
The EVS snapshot function is currently in Open Beta Test (OBT), and you can use the function for free.

EVS provides you with the encryption function. You can encrypt newly created EVS disks.
EVS uses the industry-standard XTS-AES-256 encryption algorithm and keys to encrypt EVS disks. Keys used by encrypted EVS disks are provided by the Key Management Service (KMS) of Data Encryption Workshop (DEW), which is secure and convenient. Therefore, you do not need to establish and maintain the key management infrastructure.

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

Through the EVS disk transfer function, EVS disks can be transferred from one tenant to another. After the transfer succeeds, the ownerships of the EVS disks belong to the target tenant only. Currently, only data disks can be transferred.
You can call APIs only to use the disk transfer function.

Tags identify EVS resources for purposes of easy categorization and quick search.
You can add or modify tags to an EVS disk during or after EVS disk creation.

Cloud Eye on HUAWEI CLOUD provides you with insights into the running statuses of your EVS disks.

You can use Cloud Eye to automatically monitor EVS disks in real time and manage alarms and notifications to keep track of EVS performance metrics.

Cloud Trace Service (CTS) is a log audit service. You can use CTS to trace operations in EVS disks.

All cloud service resources have quotas to prevent unforeseen spikes in resource usage. Quotas can limit the number and capacity of resources available to you, such as the number of EVS disks, the capacity of EVS disks, and the number of EVS snapshots.
You can also request for an increase in quota if the existing quota does not meet your service requirements.

After an EVS disk is created, you can change the disk type as needed. The new disk type must have a higher specification. For example, a high I/O disk can be changed to an ultra-high I/O, extreme SSD, or general purpose SSD disk, but cannot be changed to a common I/O disk.