Storage VMotion Latency Limitations

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    Latency

    • Latency measures delays in data flow.Photos.com/Photos.com/Getty Images

      Latency refers to delays in transmitting and receiving data. Latency can be caused by limited bandwidth that delays the transmission of information or limited availability of processing resources. Latency is increased when a computer is heavily used, taking up memory and CPU capacity. Latency increases when data storage limitations are reached. Latency problems can paralyze a computer network and prevent a VMware machine from accessing its data storage location.

    Fault Tolerance Mode

    • Fault tolerance (FT) in VM is a mode designed to ensure up time for mission critical virtual machines. Constant and ongoing backups called synchronization are run using VMotion to prevent data loss. Network and computer latency causes delays in synchronization and can interfere with fault tolerance mode. Use of fault tolerance fails when the data storage location cannot be accessed, either due to latency issues or network hardware failure.

    Methods to Improve VMotion Latency

    • VMotion migrations can fail when VM is too active, using resources critical to the migration. Wait until there is less VM activity to perform a migration. Schedule migrations for times when most users are not on the network. Putting VMotion network traffic on its own network reduces latency. VMotion contains a throttle that can be slowed, reducing latency on the network due to decreased demand from the VM instances. Increasing the number of data ports provides more communication channels, reducing latency if it is caused by limited bandwidth and communication points with the VM data storage locations.

    VMware Latency Improvement Methods

    • VMware ESX is called a hypervisor. It manages computer virtualization across an entire enterprise between ESX hosts. The das.failuredetectioninterval setting in vCenter measures the heartbeat between ESX hosts. The default detection interval is every second. Increasing the detection interval reduces traffic on the network, decreasing latency. Storage I/O Control (SIOC) controls the priority of access to storage I/O. Administrators can assign higher-priority access for VM shares to storage I/O to reduce VM latency. Increase guest-level latency and decreasing guest-level bandwidth to data stores. This prevents Storage VMotion workload from causing latency problems with general VMware data transfers. Increase the VM preference to CPU and memory resources on a hard drive to reduce latency.

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