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General inquiries Registration Billing, subscriptions and Fapiao Implementation and maintenance Show all

1 General Inquiries

  • What is Azure?

    Azure is a flexible and open cloud platform that enables you to quickly build, deploy, and manage applications in the data centers. Azure supports all major operating systems, languages, or development tools and integrates public cloud applications with the existing IT infrastructure.

    Azure offers international class Service Level Agreements that enable you to build and run highly available applications without having to focus on the infrastructure. It provides the ability to automatically repair operating systems and services, and has built-in network load balancing and hardware fault recovery capabilities. It supports the deployment models that allow you to upgrade applications with no downtime.

    Azure enables you to generate applications in any language and by any framework or tool. Azure utilizes the public functions and services of open REST protocol. Azure’s client libraries are available in a variety of programming languages and are published under open source licenses and hosted on GitHub.

    Azure offers a flexible cloud platform that meets the needs of any application.

  • What are the prices of Azure services in China?

    We will continue to update and release more information on pricing. You can get the latest information on the Pricing Page.

  • Are Azure services in China the same as Azure services in other areas?

    In China, Azure is operated by Shanghai Blue Cloud Technology Co., Ltd., a wholly-owned subsidiary of Beijing 21Vianet Broadband Data Center Co., Ltd. (abbreviated as "21Vianet"). 21Vianet is China’s largest neutral third-party Internet infrastructure service telecommunications provider to which Microsoft has authorized technologies. In China, Azure combines Microsoft’s global technologies and 21Vianet’s local operating experience to build an enterprise-level international cloud computing platform for China.

    Outside China, Microsoft Azure is operated by Microsoft itself. China’s Azure customers will be able to enjoy exactly the same user experiences and service level as customers in other areas.

  • What is an SLA (Service Level Agreement)? What kind of SLA does Azure offer in China?

    We provide international class Service Level Agreements for each of the Azure services that are officially available for commercial use. If a certain service level is not reached, the customer can receive the corresponding service fee deduction. Details on SLAs provided by Azure in China are listed at: Service Level Agreements.

  • What are some success stories of Azure in China?

    In China, a large number of enterprises like GMW.cn, Linekong, Spring Airlines, Mobike, Digital China, Coca Cola, Kingdee, PPTV, ChinaCache, and Qoros have landed onto the Azure platform in China. Please go to the Success Stories page for more information on these cases.

  • How is Virtual Machines charged? Why does my virtual machine still incur costs when it’s stopped?

    Virtual Machines billing consists of two parts: the cost of the virtual machine itself and the cost iccurred by its disk (including managed disk and non-managed disk), so as long as your virtual machine and the disk are not deleted, disk storage cost always exists. Please refer to the Price Details of Disc Storage for billing details.

    In addition, note that the two virtual machine statuses "Stopped" and "Stopped (de-allocated)" are charged differently. Please refer to the following table:

    Status Virtual Machine cost Disc cost Detailed information
    Starting Up Yes Yes This is the initial starting state of the virtual machine, during which the virtual machine is going through a startup cycle and is charged as normal, as the virtual machine is running.
    Running (already started) Yes Yes The virtual machine is running and charged as normal.
    Stopped Yes Yes The shutdown operation is performed through the virtual machine, and the virtual machine will be in a "Stopped (de-allocated)" state. During this time, the core is not released, so the virtual machine is still being charged.
    Stopped (de-allocated) No Yes The shutdown operation is performed through the Azure portal, and the virtual machine will be "Stopped (de-allocated)". During this time, the computing resources will no longer be allocated to the virtual machine, so the virtual machine will no longer be charged for it. However the cost of disk storage still exists, as the disk still exists.
    Deleted (including the disk) No No You should ensure the disk has been deleted while deleting the virtual machine. Otherwise, there will still be disk storage costs.
  • How do I select Azure computing services: Web Apps, Cloud Services or Virtual Machines? If I’m an enterprise user, which services should I select to migrate the existing enterprise applications to the Azure cloud computing platform when provided with these three different computing capabilities?

    According to the following characteristics, you can select the service that is suitable for your needs:

      Characteristics Suitable For
    Web Apps
    1. You can easily deploy a highly scalable cloud environment by building a highly scalable website on Azure, which can start at a very small scale.
    2. You can use language and open source applications of your own choice, such as WordExpress, FTP, Git or TFS, and easily integrate them with Azure services, such as SQL databases, caches, CDN and storage.
    1. Modern Web Apps. Include client scripts, server-side scripts and database applications, and can be scaled horizontally.
    2. Continuous development. You can use Git or Team Foundation directly from the source code libraries for deployment.
    3. Using open source applications. You can directly use open source applications, such as WordPress.
    Cloud Service
    1. Expand your enterprise applications on Azure.
    2. A rich PaaS environment can be utilized to create highly available and scalable applications and services. Advanced multi-layer architecture, automatic deployment and elastic computing are supported.
    3. Through a virtual network, you can connect the network of the local LAN to the Azure public cloud network to allow the enterprise network to enjoy the highly elastic computing and interoperability brought by the public cloud, while ensuring network security.
    1. For multi-layer applications, each layer can expand itself. When using Web Role and Worker Role, Web Role can respond to the display at the front end, while the complex business is handled at the back end.
    2. Advanced management. You can use Cloud Service if your application requires administrator rights, remote desktop access, or escalated authority to run the code.
    3. Private cloud + public cloud. You can use Azure Connect for point-to-point connection with Azure or use the Azure virtual network to connect the enterprise internal or private network to Azure.
    Virtual Machines
    1. IaaS service is provided. Windows and Linux operating systems are supported
    2. You can easily deploy and run Windows Server and Linux virtual machine and migrate the operating load in a few minutes, without changing the existing code. For applications based on Windows OS, you can deploy them to Hyper-V, save it as a VHD file and upload it to Azure for deployment and management.
    3. Virtual network supported. You can connect your LAN enterprise application with the public cloud directly and enjoy the convenience of cloud computing.
    1. Windows or Linux supported. You can quickly migrate the existing Windows or Linux applications to Azure.
    2. More service applications are supported. You can use SQL Server, MySQL, MongoDB, and SharePoint applications in Azure.
    3. Migrating existing applications to the public cloud is supported. You can save persistent non-relational data in Azure VHD.
  • How do Azure services in China ensure the security of users’ data and services?

    Security and stability of Cloud Services have always been the focus of the industry. As the first international public cloud service landed in China, Microsoft Azure operated by 21Vianet has gained recognition from many industry users, and provided users with reliable, flexible and highly valuable public Cloud Services.

    Being the first to land all-round cloud services including IaaS, PaaS, SaaS in China , and reliable localized operation, international standard monthly Service Level Agreements with financial security, powerful data security, rich client returns and other advantages, Microsoft Azure operated by 21Vianet has obtained 6 credible cloud certifications including Yunfen, Cloud Engine (Cloud Services) and the Whole Network Load Balancing (Traffic Manager), representing recognition from the industry for the quality of localized international cloud service provided by 21Vianet.

    Moreover, according to the GBT 22240-2008 Information Security Technology - Guide on Determination of Security Protection Levels for Information Systems, the assessment organization authorized by the Ministry of Public Security has conducted an assessment of Microsoft Azure operated by 21Vianet as per GB/T 22239-2008 Information Security Technology - Basic Requirements of Security Protection Levels of Information Systems. The Information Security Protection of Azure has been classified as the third Level (Information System Classified Security Protection (DJCP), Level 3) and has been issued with record-keeping certificates.

    In full compliance with China’s policies and regulations, Azure data service in China provides up to six geo-redundant backups, which are distributed in 2 data centers (China North and China East). In addition, with decades of experience in providing enterprise customers with online services applied in the Azure platform, we strive to keep the leading position in the industry in terms of security, privacy and control and compliance practices.

    For more details, see the Data Security, Privacy and FAQ pages in the Azure Trust Center.

  • I have an MSDN subscription, and when I enable "Azure Benefit" for my account, can this service be available in Azure China at the same time?

    No. China's Azure service is operated by 21Vianet. The "Azure Benefit" in your account can only be operated on platforms in other areas of Azure. MSDN accounts cannot be enabled on Azure China's platform operated by 21Vianet. If you’re interested in applying for one of the Microsoft Azure services operated by 21Vianet, please fill out the Azure Trial Application Form to experience Azure with the 1RMB Trial plan.

  • Does Azure support open-source software in China?

    Azure supports a large number of open source applications, frameworks and languages, and the number is still growing. We understand that developers want to use the most suitable tools based on their own experience, skill, tool and application needs, and our goal is to allow developers to choose tools as needed.

    For open source code, please refer to Microsoft Azure SDK.

  • What kind of roles does Microsoft play in Microsoft Azure operated by 21Vianet?

    Microsoft Azure in China is a public cloud platform that is operated and sold independently by 21Vianet in China mainland. Based on Microsoft's decades of rich online service experience for global enterprise customers, Azure, a world-class technology, is developed to fully serve customers in China, and guarantee to provide globally consistent service quality for our customers all over the world.

  • Where can I find details on the new features?

    You can find the details of the new features through the What's New.

  • How will 21Vianet use the information I stored in Azure?

    21Vianet will only use the customer data you stored in Azure to provide you with Azure services. These services may include the troubleshooting for preventing, detecting, or fixing issues that affect the operation of Azure; and also the improvement of features that detect and resist emerging and evolving threats to users (such as malicious software and junk mail).

    As per 21Vianet policy, in addition to providing you with cloud productivity services, we will never mine or use your customer data for advertising purposes. If you want to know more about our commitment regarding your data, please go to the Privacy and FAQ pages in the Azure Trust Center.

  • I want to learn more about Azure. In addition to the Starter Guide, do you have any further study materials?

    You can browse the Documentation Center.

    This page contains links and the following content:

    • Developer center: .NET, Node.js, Java, Python
    • Details of various services: computing, data services, app services, network
    • Multiple resources: architectural structure, reference documentation, advice on effective use, performance, and answer to questions, etc.

    Publish and search questions in the Azure Forum.

    Browse the Azure School for related Azure courses and expert columns.

Registration Questions

Billing, subscription and Fapiao

Implementation and Maintenance

  • During the maintenance period, how long will a single IaaS virtual machine or single PaaS role instance stay offline?

    Answer: For IaaS Virtual Machine or PaaS role instance, it requires about 15 minutes for self-service maintenance, and 30–45 minutes for planned maintenance.

  • If my Virtual Machine is impacted for a relatively short time, can I define the maintenance time on my own?

    Answer: Yes. For maintenance requiring restarting the virtual machine, customers will be informed by the system in advance. The planned maintenance has two stages: self-service maintenance by the user and maintenance by the system. Customers can check the status of the virtual machine, start self-service maintenance and restart the virtual machine in the self-service maintenance stage. Please refer to Maintenance and Updates for Azure Virtual Machines and Maintenance in the Plan for more information about the maintenance of virtual machines.

  • Can I opt to have my virtual machine exit this maintenance?

    Answer: You may achieve this by shutting down the virtual machine during the whole maintenance stage.

  • What measures should I take to reduce the impact and risk on production applications caused by this maintenance?

    Answer: We recommend that you use the Availability Set in the architecture to ensure continuity of business. For Cloud Services and Virtual Machines in an Availability Set, maintenance updates only one instance of an Update Domain (UD). We also encourage customers to cooperate with Microsoft contacts (sales field staff, technical account managers, etc.) on Availability Set. For more information, please visit the Virtual Machine Management Availability web page.

  • Why can’t I access the VIP IP address and ports of Azure VM from the local Ping?

    When accessing a virtual machine via a VIP address, network traffic needs to go through Azure Load Balancer. Azure Load Balancer currently blocks the ICMP protocol. Ping belongs to the ICMP protocol group and cannot get through the Load Balancer. If customers need to verify the connectivity of virtual machines via VIP, they can do it with tools based on TCP Protocol. For more information, please refer to Using the PsPing & PaPing for TCP port connectivity testing.

  • Can I create a virtual machine inside Azure Virtual Machine?

    No, you cannot create it at present. The Dv3 and Ev3 series Azure Virtual Machine support nested virtualization, but as of now, Azure China does not support creating virtual machines of these series for the time being.

  • Can I create a Windows Server 2003 virtual machine in Azure?

    The officially supported Windows Server virtual machine templates are:

    • Windows Server 2008 R2
    • Windows Server 2012, Windows Server 2012 R2
    • Windows Server 2016

    Customers can create their own virtual machine template locally on Hyper-V for Server 2003 and upload it to Azure cloud, but Microsoft does not provide official support if there’s any problem with virtual machines created this way.

  • Is it supported to deploy Microsoft Exchange, Lync and Sharepoint in Azure?

    The SharePoint Virtual Machine templates can be selected from Azure Virtual Machine templates and can be officially supported by Microsoft. Exchange Server and Lync Server can be customized and uploaded, but not officially supported.

  • What is the load balancing mechanism?

    Azure Load Balancer is based on the fourth layer protocols (TCP, UDP), serving to distributing incoming traffic to the well-operating service instances defined in a load-balancing set, so as to improve the availability and network performance of applications.

    Azure Load Balancer can be configured to:

    • perform load balancing on Internet traffic going to the virtual machine. This configuration is called Internet-facing load balancing.
    • perform load balancing on network traffic among virtual machines in the virtual network, network traffic among virtual machines in the Cloud Services, or network traffic between local computers and cross-premises virtual networks. And this configuration is called Internal Load Balancer.
    • forward external traffic to designated virtual machines.

    For more details about Azure Load Balancer, please refer to Overview of the Azure Load Balancer.

  • How do I perform data backup?

    Azure backup provides two types of redundancy: Local Redundant Storage (LRS) and Geo-Redundant Storage (GRS). Local Redundant Storage copies the data in the matching data centers of the same region three times (creating three data copies). Geo-Redundant Storage copies the data to a secondary region several kilometers from the primary location of the source data. In order to prevent temporary storage unavailability arising from a disaster in one region, we recommend that customers back up their data using Read/Access Geo-Redundant Storage (RA-GRS). This way, in case of unavailability of the storage account of the primary region, the data can be accessed from the secondary region.

    The following table describes backup and disaster recovery capabilities of different data services in Azure, as well as the corresponding backup methods:

    Service Name Local data redundancy mode Local backup Remote data mirroring Backup methods
    Storage service 3 copies, Active-Active None Asynchronous replication to the remote location, RPO=30 minutes, no RTO
    1. Local Redundant Storage (LRS)
    2. Zone Redundant Storage (ZRS)
    3. Geo-Redundant Storage (GRS)
    4. Read/Access Geo-Redundant Storage (RA-GRS)
    5. Use AzCopy
    SQL Database 3 copies, one master and two backups No (new function in development) None
    1. Use Azure portal
    2. Use SQLPackage utilities
    3. Use SQLDatabaseBackup scripts
    4. Use PowerShell
    IaaS virtual machine OS disk and mounted disk Only preserves data, same as storage service None Only preserves data, same as storage service
    1. Azure Backup
    2. Azure Site Recovery
    3. Managed Snapshot
    4. Database in IaaS virtual machines. Customers can use various database backup tools or back up the file by exporting the database
    IaaS virtual machine temporary disk None None None None
    PaaS Cloud Services, mobile services and Web Apps Only preserves published packages and code None None Backup options on the Azure portal application page
  • Can I specify regions (China East, China North) for VIP addresses when creating related services (Cloud Computing)?

    VIP address is determined in accordance with the selected region (China North, China East) of the services being created and is randomly assigned from the IP address pool managed by Microsoft. For instance, if the customers choose China North, they will be preferentially assigned within an IP address in China North.

  • What should I be aware of when running a business application on a virtual machine?

    Azure will regularly update the host environment to ensure that all the applications and virtual machines on the platform are always in a secure environment. This update process may cause your virtual machines to reboot. Rebooting of the virtual machines will cause applications on these virtual machines to go offline.

    There may be data lost during virtual machine migration. Some reasons for virtual machine migration are as follows:

    • Adjusting the size of the virtual machine
    • Updating the host
    • Hardware failure on the host
    • User configures AutoScale for automatic expansion and contraction

    In order to guarantee high availability of applications/services hosted in Azure virtual machines, we recommend:

    • 1. Use multiple virtual machines in an Availability Set.

    • 2. Deploy high availability structure for all components (front-end interface/application logic/data storage, etc.) of the pplications; Deploy each component on multiple virtual machines in Availability Sets, so that any individual virtual machine involved in the application deployment going offline does not bring the entire system offline.

    • 3. After the key business applications are deployed to Azure Virtual Machines, test the applications thoroughly for the potential impact of virtual machine reboot.

    For more information, please refer to the following links:

    Manage Availability of Windows Virtual Machine on Azure

    Why are Azure VMs rebooted ?

    Service Level Agreement

  • What should I be aware of about using virtual machines to store application data?

    Azure Virtual Machine disks include a temporary disk, the D: disk (Windows) or /dev/sdb1 (Linux). They only provide temporary storage, so there is a risk of data loss, and the data cannot be completely recovered under some conditions. It is recommended against to use the disk to store data that require long term preservation, otherwise users must bear the risk of data lost resulting from this. Data loss on temporary disk usually occurs when virtual machines are migrated to different hosts. Reasons for virtual machine migration include: adjustment of virtual machine size, host update, or failures in host hardware. Exact time of virtual machine migration cannot be predicted, and it is very likely to occur without any user operation. For more information on virtual machine disks and high availability, refer to the following links:

    About disk storage of Azure Windows VM

    Manage Availability of Windows Virtual Machine on Azure

    Why are Azure VMs rebooted ?

    Service Level Agreement

  • How do I add virtual machines into a virtual network? What is the difference whether or not adding virtual machines into a virtural network? And how do I put an existing virtual machine into a new virtual network?

    First, create a virtual network; select the previously-created virtual network when creating a virtual machine; add the virtual machine to the virtual network. For detailed steps, please refer to How to Add the Virtual Machines to the Virtual Network.

    When adding into virtual networks, virtual machines can guaranteed to communicate with each other via intranet, and advanced functions, such as P2S and S2S VPN, can be configured.

    If a virtual machine is not added to a virtual network during creation, it cannot be added to a virtual network later. Currently, the only approach is to delete the virtual machine (select to save the data disks), create a new virtual machine from the previously saved data disk, and choose to join an existing virtual network during the creation.

  • How to configure websites deployed in Azure virtual machine to be accessible from public networks?

    By default, Azure virtual machines only open limited ports corresponding to its VIP, used for remote connection or management. If a newly built website needs to be accessed via a certain port of a VIP, it is required to add an Endpoint to this virtual machine. This operation can be completed through Azure portal or Powershell.

  • What is availability set? How do I use availability set to increase the availability of applications?

    Availability set is a type of logical grouping function. Applying it in Azure ensures that VM resource are mutually isolated after deployment.

    Azure can ensure that the VM deployed in availability sets can run across multiple physical hosts, computer racks, storage units and network switches. In case of hardware failure, Azure software issue, or VM and applications update, only part of the VM will be affected and the applications as a whole can maintain functional for users.

    For more details, please refer to Azure IaaS User Manual and How to use Availability Set.

  • How about the security of the Azure Storage service?

    Azure Storage service will allocate two access keys to users: the primary and secondary access keys. Each of the access keys is a character string with 256 bytes, and user can use it to verify every data access request for Azure Storage services.

    Both access keys have the same function and are able to access the data. The main purpose of having two keys is to for users' convenience when switching access keys. For instance, users will normally use the primary access key. If the primary access key is stolen, user can set the primary access key immediately (a new primary access key will be generated), and then switch over to the secondary access key. Meanwhile, user does not have to revise code for this, but only needs to change the service configuration file, without any downtime. Moreover, another effective way is, application code can use the primary access key to access data, and if the verification fails, the code will automatically use the secondary access key. This way, there will be no downtime when user switches access keys.

    In order to further increase flexibility of access control for Blob data, Azure Data Storage service provides another data access control method, Shared Access Signature. Administrators can use Shared Access Signature to generate a temporary data access request for other users, which contains valid digital signatures, and can thus pass the data verification. It also contains information about user's permission for data access and operation. The temporary request will only be effective within the specified timespan. This way, administrators can allow other users to access data, without leaking the access key.

  • What is the difference between Azure SQL Database and the traditional SQL Server Database?

    Though SQL Server and Azure SQL Database sometimes handle the same application working load, one is a traditional database server under the software licensing model, while the other one is under the service-model cloud database running in the data center of 21Vianet, and is available as a pay-as-you-go model or a commitment rate model. You can easily choose the platform and business model that best suits your technological requirements between these two products.

    SQL Server Azure SQL Database
    SQL Server is an enterprise-level database server, which is able to provide "vertical scalable" relational data storage and handle a wide-range of internally deployted applications and scenarios. SQL Server is not a service product and does not use a pay-as-you-go consumption model. SQL Server is licensed per server or per processor, and involves a rich set of server hardware. SQL Server runs on the hardware in your data center or your hosting provider's data center. Azure SQL Database is a highly-available distributed "horizontal scalable" database service, hosted in the Cloud operated by 21Vianet. With Azure SQL Database, users can easily configure and deploy the relational database as a service. Developers or administrators do not have to install, configure, patch or manage any software. This service has built-in high availability, backup and recovery, geographical distribution, and disaster recovery.

    In addition to the difference between vertical/horizontal scaling, there are major differences in operating modes. Azure SQL Database service covers management of hardware and operating system, and therefore users can focus on building the solutions instead of purchasing, managing, patching, and licensing the hardware, virtual machines, operating systems and application platform software. However for the dedicated database servers (whether installed as traditional servers in on-premises deployment, hosted in the virtual machine, or hosted by the third-party service provider), developers and IT professionals are still responsible for installing, configuring, updating, and patching the operating system and database software. Furthermore, users of the database server must design their own solutions for high availability, vertical scaling and disaster recovery, resulting in increased overall management costs.

    Azure SQL Database is targeted at designing and optimizing applications towards high scalability and high availability at a lower cost than a traditional vertical-scaling structure. As a result, Azure SQL Database is able to provide highly-available vertical-scaling solutions on commercial hardware and provide database functions as a service.

    For more details, please refer to the SQL Azure web page.

  • How is Azure’s data redundancy guaranteed?

    We provide geo-redundancy. One dedicated line is used to connect the two data centers in Beijing and Shanghai. It is dedicated to data synchronization between the data centers. In terms of data storage, Azure provides four redundancy levels for storage:

    • Local Redundant Storage (LRS): we maintain multiple data replica in a region so as to provide high durability.
    • Geo-Redundant Storage(GRS): we provide extra data durability through asynchronous replication between two regions hundreds of miles apart. In the two regions, we maintain multiple data replicas.
    • Read-Access Geo-Redundant Storage (RA-GRS): in addition to GRS services, we provide read-only access to the storage account in the secondary region (which has a final edition consistent with data in the primary region). When the storage account in the primary region is not available, customers can use this service to access the data.
    • Zone Redundant Storage (ZRS): in addition to storing three replicas like LRS, ZRS replicates data asynchronously between data centers of one or two zones, providing a higher durability than LRS.

    For details on Azure Redundant Storage, please refer to Introduction to Azure Storage and Pricing Details.

  • Are all data stored in Azure encrypted?

    Regarding data encryption, Azure provides all kinds of encryption functions including AES-256, allowing customers to choose the best solutions based on their requirements.

  • What cloud and data security certifications has Azure obtained in China?

    Azure has obtained the following cloud and data security certifications in China:

    ISO/IEC 27001:2005 auditing and certification

    21Vianet commits to perform the authentication in accordance with the ISO/IEC 27001:2005 (this is a broadly applied international information security standard). ISO/IEC 27001:2005C Certificate has confirmed that 21Vianet has carried out information security control measures defined in this Standard and recognized internationally, including guidelines and general principles on starting, implementing, maintaining, and improving information security management in the organization.

    ISO scope: The Information Security Management System (ISMS), covering operations, security and management of commercial procedures.

    The certificate is openly issued by the CESI Certification Co., Ltd. (CESI).

    Trusted Cloud Services Certification

    21Vianet has adopted Azure’s leading technology, and with its strong capabilities in localized operation, open platform, high-quality SLA (Service Level Agreement), strong data recovery ability and best customer benefits, the company was among the first batch to be successfully certified the Trusted Cloud Services for Virtual Machines and Storage services.

    The Trust Cloud certification is the quality assessment system of the Cloud Services under the direction ob the Ministry of Industry and Information Technology of the People’s Republic of China, organized and implemented by the Cloud Computing Development and Policy Forum - the "Trust Cloud Group". This certification aims to cultivate the domestic public cloud service market, enhance user confidence in Cloud Services, protect the formal cloud service providers, and promote sound development of the market.

    Scope: The following functions are currently in audit: Virtual Machines and Cloud Storage, accepting the assessment of 16 indicators in three large categories: data management, business quality, and rights guarantees within the SLA framework. Among these, Microsoft Azure virtual machine and cloud storage service provided by 21Vianet have achieved a 99.9% SLA guarantee in terms of operation stability.