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Introduction to VMotion

2025-01-25 Update From: SLTechnology News&Howtos shulou NAV: SLTechnology News&Howtos > Servers >

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Origin: according to hearsay, VMotion is one of the features of VMware. Based on this, dynamic migration, DRS,HA and other functions are realized above, but what is the underlying principle?

What is VMotion?

VMotion allows virtual machines to dynamically migrate from one physical host to another, and ensures that the migration process 0 stops, does not stop service, and ensures transaction integrity.

When a virtual machine migrates from one physical host to another and keeps it running, how do you do it?

How does VMotion work?

As a prerequisite, multiple physical ESXI hosts share a set of storage, and all ESXI hosts connected to this set of storage can read and write virtual machine files.

First, VMotion sets up a set of "Shadow Copy" of the source virtual machine on the destination host, which is used to receive the memory data of the source virtual machine.

Then, VMotion creates a set of system snapshots of the source virtual machine, commonly referred to as "PreCopy." And the PreCopy is quickly transmitted to the target host over the Ethernet network. At the same time, VMotion establishes a set of change log buffer to store the memory changes of the source virtual machine at this time, and the VMotion continuously transmits the changes to the destination host until the next set of change data is less than 500ms. VMotion closes the source virtual machine CPU, transfers the last piece of change log buffer to the destination virtual machine, cuts off the disk access of the source virtual machine, and opens the disk access of the destination virtual machine. Finally, start the CPU of the destination virtual machine.

Finally, VMotion notifies the destination virtual machine to send a RARP packet, informing the switch in the network to update its MAC address-physical address mapping. As a result, all traffic is forwarded to the correct interface.

The virtual machine MAC address remains the same during the hot migration, but cloning the virtual opportunity causes the destination virtual machine MAC address to change.

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