Zero Downtime: In-Depth Analysis of 4 Virtualization Hot Migration Core Technologies and Practices

VMware virtual machine migration typically includes cold migration and hot migration methods, with hot migration being the preferred solution for online businesses as it ensures business continuity.

Migrating from VMware to new platforms has become a priority for many enterprise technology decision-makers, primarily due to Broadcom’s adjustments to VMware’s product sales model which have significantly increased user costs. According to CRN, Toshiba – a 16-year VMware user – decided to switch platforms after discovering related product costs had surged to 10 times the original price, and is currently migrating 2,200 virtual machines from the VMware-Broadcom platform to alternative platforms.

When migrating from existing virtualization platforms (such as VMware) to other cloud platforms, several questions arise: How to ensure data security and integrity? How to minimize downtime? What migration tools and operational guidelines are available for processes like VMware-to-ZStack platform migration? Among these considerations, hot migration technology is undoubtedly key to achieving these goals.

The Importance of Hot Migration: The Cornerstone of Business Continuity

Hot migration, as the name suggests, refers to the technology of seamlessly transferring virtual machines from one physical host to another without interrupting their operation or services. This contrasts sharply with cold migration which requires shutting down or pausing services. Its core value lies in ensuring zero business downtime. For enterprises, hot migration is not only a powerful tool for routine operations and maintenance (such as hardware upgrades, load balancing, and system maintenance) but also an indispensable component for building highly available and resilient data centers. Especially when facing large-scale data center consolidation or platform migrations like VMware-to-ZStack, hot migration can significantly reduce business risks, improve user experience, and ensure continuous operation of core business services. ZStack’s VMware-to-ZStack Solutions cover three major paths: server virtualization, enterprise cloud, and hyperconvergence, having successfully helped over 600 enterprise customers transition from VMware.

Analysis of Core Technologies for Virtualization Hot Migration

To achieve zero-downtime hot migration, virtualization platforms need to integrate multiple complex technologies. Below we will explore the principles of several mainstream virtualization hot migration core technologies.

1. Pre-Copy Based Memory Migration

This is the most common hot migration technology. At the start of migration, the virtual machine continues running while its memory data is copied in batches to the target host. During this process, since the virtual machine remains operational, its memory may change. Therefore, the system continuously tracks these changes and in subsequent iterations only transfers the modified memory pages (dirty pages). When the number of transferred dirty pages reaches an acceptably small threshold, the virtual machine will pause for an extremely short time (millisecond level), synchronize the final remaining dirty pages to the target host, and then resume operation on the target host. This method minimizes service interruption time and is key to achieving zero downtime.

2. Post-Copy Based Memory Migration

In contrast to pre-copy, post-copy technology first quickly transfers the virtual machine’s CPU and essential state information to the target host and immediately starts the virtual machine there. At this point, some of the virtual machine’s memory may not yet be fully copied to the target host. When the virtual machine needs to access a memory page that hasn’t been migrated, it triggers a page fault interrupt, and the target host then copies that memory page on demand from the source host. This method allows faster initiation of the migration process but may result in more page fault interrupts during the early migration phase, causing performance fluctuations.

3. Shared Storage Hot Migration

This migration approach requires that the virtual machine’s data disks (storage) reside on shared storage accessible to both source and target hosts. Therefore, during hot migration, only the virtual machine’s computational state (CPU and memory) needs to be migrated, eliminating the need to copy large amounts of storage data, which greatly simplifies the migration process and improves efficiency. ZStack Software-Defined Storage supports storage resource pools exceeding PB-level capacity, providing a solid foundation for this hot migration mode.

4. Network-Assisted Hot Migration

Some advanced hot migration technologies utilize network optimization and intelligent scheduling to improve migration efficiency. For example, by implementing data compression, deduplication, or priority control at the network level to reduce bandwidth consumption during migration. Meanwhile, intelligent scheduling algorithms select optimal migration paths and timing based on factors like host load and network conditions, ensuring a seamless migration process.

ZStack Empowering Hot Migration Practices

ZStack deeply understands enterprise needs during hot migration and platform transitions, and thus its product system is designed to efficiently and securely support various complex migration scenarios. Particularly, the ZStack ZSphere virtualization platform provides a user experience consistent with VMware virtualization products, supporting intelligent unified operations, seamless V2V migration, and offering high stability and security, making it an ideal choice for hot migration. ZStack ZSphere product videos also demonstrate its virtual machine migration capabilities, including live migration, cross-cluster/data center migration, and failure-driven migration scenarios.

ZStack’s “4S” features – Simple, Strong, Scalable, Smart – play crucial roles in hot migration practices:

• Simple: ZStack products are easy to install and deploy, with simple operational maintenance and user-friendly interfaces. This enables management and execution of even complex hot migration tasks through intuitive interfaces, lowering technical barriers and reducing operational error risks.
• Strong: With robust system architecture, high availability (HA) between virtual machines and management nodes, and support for high-concurrency API requests, ZStack ensures system stability and reliability during intensive operations like hot migration.
• Scalable: ZStack supports elastic deployment from single services to 10,000+ servers, with flexible expansion capabilities and compatibility with multiple systems while providing open APIs. This means ZStack can easily handle large-scale hot migration demands and achieve seamless expansion.
• Smart: ZStack offers automated operations, intelligent online upgrades, smart UI interactions, and real-time monitoring and auditing. These intelligent features help enterprises automatically identify and optimize hot migration paths, monitor migration progress and status in real-time, ensuring the entire process is seamless and efficient.

Additionally, ZStack’s disaster recovery solutions are tightly integrated with hot migration, supporting six major disaster recovery scenarios through technologies like snapshots, block data replication, CDP (Continuous Data Protection), backup, disaster recovery, and active-active configuration, ensuring enterprise data security and business continuity. Whether for resource adjustments within data centers or cross-data center application disaster recovery, hot migration is key to achieving uninterrupted business operations.

ZStack: Let Every Company Have Its Own Cloud

As a leading cloud infrastructure software provider, ZStack is committed to empowering every company to have its own cloud. Its product line covers enterprise cloud, virtualization, hyperconvergence, software-defined storage, data center management, edge orchestration, cloud-native platforms, and database management.

It’s particularly worth mentioning that ZStack is not only a leading cloud infrastructure expert but also an important AI product service provider. Through the ZStack AI Infra Platform AIOS, it fully supports enterprise AI applications in three key areas: “computing power scheduling, AI large model training and inference, and AI application service development.” ZStack has been recognized by Gartner® as a representative vendor in the “Innovation Insight for AI Infrastructure in China” report.

Currently, ZStack’s business covers more than 30 countries and regions globally, with over 10,000+ community users and 200+ partners, supporting more than 100 application scenarios, and winning the trust of 4,000+ leading enterprises. It not only provides industry-leading cloud platform products but also comprehensive service support, technical documentation, training certification, and rich customer cases, ensuring customers receive professional support at every step of their cloud transformation.

FAQs

What is hot migration? How is it different from cold migration?
Hot migration refers to the technology of seamlessly transferring virtual machines (VMs) from one physical host to another without interrupting their operation or stopping services. In contrast, cold migration requires shutting down or pausing the virtual machine before migration. The greatest advantage of hot migration is achieving zero business downtime and ensuring service continuity.

What role does hot migration play in enterprise data center operations?
Hot migration plays a critical role in enterprise data center operations, enabling administrators to perform hardware maintenance, resource optimization, load balancing, failover, and system upgrades without affecting business operations. Especially during platform migrations like VMware-to-ZStack, hot migration is one of the core technologies ensuring business continuity and data integrity.

How does ZStack ZSphere support hot migration functionality, and what are its advantages?
The ZStack ZSphere virtualization platform provides a user experience consistent with VMware, supporting intelligent unified operations and seamless V2V migration. It offers capabilities including live migration, cross-cluster/data center migration, and failure-driven migration. ZStack ZSphere’s advantages lie in its high stability, security, and ease of use. Combined with ZStack’s “4S” features, it helps enterprises efficiently and securely achieve various hot migration requirements.

What are some best practice recommendations when performing VMware-to-ZStack hot migration?
When performing VMware-to-ZStack hot migration, it’s recommended to first conduct comprehensive environment assessment and planning to ensure network connectivity and storage compatibility. Utilize ZStack’s provided VMware-to-ZStack Solutions and related product documentation/user manuals for guidance. Simultaneously, fully leverage ZStack ZSphere’s hot migration features combined with real-time monitoring and verification to ensure seamless migration processes and data consistency.