vMotion and Storage vMotion
If you have read anything about VMware, you have most likely read about the extremely unique and innovative feature called VMotion. VMotion, also known as live migration, is a feature of ESX/ESXi and vCenter Server that allows a running virtual machine to be moved from one physical host to another physical host without having to power off the virtual machine. This migration between two physical hosts occurs with no downtime and with no loss of network connectivity to the virtual machine.
VMotion satisfies an organization's need for maintaining SLAs that guarantee server availability. Administrators can easily initiate VMotion to remove all virtual machines from an ESX/ESXi host that is to undergo scheduled maintenance. After the maintenance is complete and the server is brought back online, VMotion can again be utilized to return the virtual machines to the original server.
Even in normal day-to-day operations, VMotion can be used when multiple virtual machines on the same host are in contention for the same resource (which ultimately is causing poor performance across all the virtual machines). VMotion can solve the problem by allowing an administrator to migrate any of the running virtual machines that are facing contention to another ESX/ESXi host with greater availability for the resource in demand. For example, when two virtual machines are in contention with each other for CPU power, an administrator can eliminate the contention by performing a VMotion of one of the virtual machines to an ESX/ESXi host that has more available CPU.
VMware VMotion allows users to:
Perform hardware maintenance without scheduled downtime.
Proactively migrate virtual machines away from failing or underperforming servers.
Automatically optimize and allocate entire pools of resources for optimal hardware utilization and alignment with business priorities.
Live migration of a virtual machine from one physical server to another with VMware VMotion is enabled by three underlying technologies.
VMware VMotion moves live, running virtual machines from one host to another while maintaining continuous service availability.
First, the entire state of a virtual machine is encapsulated by a set of files stored on shared storage such as Fibre Channel or iSCSI Storage Area Network (SAN) or Network Attached Storage (NAS). VMware vStorage VMFS allows multiple installations of VMware ESX to access the same virtual machine files concurrently.
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Second, the active memory and precise execution state of the virtual machine is rapidly transferred over a high speed network, allowing the virtual machine to instantaneously switch from running on the source ESX host to the destination ESX host. VMotion keeps the transfer period imperceptible to users by keeping track of on-going memory transactions in a bitmap. Once the entire memory and system state has been copied over to the target ESX host, VMotion suspends the source virtual machine, copies the bitmap to the target ESX host, and resumes the virtual machine on the target ESX host. This entire process takes less than two seconds on a Gigabit Ethernet network.
Third, the networks being used by the virtual machine are also virtualized by the underlying ESX host, ensuring that even after the migration, the virtual machine network identity and network connections are preserved. VMotion manages the virtual MAC address as part of the process. Once the destination machine is activated, VMotion pings the network router to ensure that it is aware of the new physical location of the virtual MAC address.
Since the migration of a virtual machine with VMotion preserves the precise execution state, the network identity, and the active network connections, the result is zero downtime and no disruption to users.
Storage VMotion builds on the idea and principle of VMotion, further reducing planned downtime with the ability to move a virtual machine's storage while the virtual machine is still running. Deploying VMware vSphere in your environment generally means that lots of shared storage-Fibre Channel or iSCSI SAN or NFS-is needed. What happens when you need to migrate from an older storage array to a newer storage array? What kind of downtime would be required?
Storage VMotion directly addresses this concern. Storage VMotion moves the storage for a running virtual machine between datastores. Much like VMotion, Storage VMotion works without downtime to the virtual machine. This feature ensures that outgrowing datastores or moving to a new SAN does not force an outage for the affected virtual machines and provides administrators with yet another tool to increase their flexibility in responding to changing business needs.
Storage vMotion is used in the following way:
Simplify array migrations and storage upgrades. The traditional process of moving data to new storage is cumbersome, time-consuming and disruptive. With Storage VMotion, IT organizations can accelerate migrations while minimizing or eliminating associated service disruptions, making it easier, faster and more cost-effective to embrace new storage platforms and file formats, take advantage of flexible leasing models, retire older, hard-to-manage storage arrays and to conduct storage upgrades and migrations based on usage and priority policies. Storage VMotion works with any operating system and storage hardware platform supported by VMware ESX, enabling customers to use a heterogeneous mix of datastores and file formats.
Dynamically optimize storage I/O performance. Optimizing storage I/O performance often requires reconfiguration and reallocation of storage, which can be a highly disruptive process for both administrators and users and often requires scheduling downtime. With Storage VMotion, IT administrators can move virtual machine disk files to alternative LUNs that are properly configured to deliver optimal performance without the need for scheduled downtime, eliminating the time and cost associated with traditional methods.
Efficiently manage storage capacity. Increasing or decreasing storage allocation requires multiple manual steps, including coordination between groups, scheduling downtime and adding additional storage. This is then followed by a lengthy migration of virtual machine disk files to the new datastore, resulting in significant service downtime. Storage VMotion improves this process by enabling administrators to take advantage of newly allocated storage in a non-disruptive manner. Storage VMotion can also be used as a storage tiering tool by moving data to different types of storage platforms based the data value, performance requirements and storage costs.
VMware Storage VMotion allows virtual machine storage disks to be relocated to different datastore locations with no downtime, while being completely transparent to the virtual machine or the end user.
Before moving a virtual machines disk file, Storage VMotion moves the "home directory" of the virtual machine to the new location. The home directory contains meta data about the virtual machine (configuration, swap and log files). After relocating the home directory, Storage VMotion copies the contents of the entire virtual machine storage disk file to the destination storage host, leveraging "changed block tracking" to maintain data integrity during the migration process. Next, the software queries the changed block tracking module to determine what regions of the disk were written to during the first iteration, and then performs a second iteration of copy, where those regions that were changed during the first iteration copy (there can be several more iterations).
Once the process is complete, the virtual machine is quickly suspended and resumed so that it can begin using the virtual machine home directory and disk file on the destination datastore location. Before VMware ESX allows the virtual machine to start running again, the final changed regions of the source disk are copied over to the destination and the source home and disks are removed. This approach guarantees complete transactional integrity and is fast enough to be unnoticeable to the end user.