VMware HA
· Function: Provides automatic failover in a cluster of ESX Server hosts to ensure high availability of virtual machines.
· Advantage:
o Cost-effective and suitable for all applications.
o No dedicated backup hardware required.
o Without the cost and complexity of clustering software.
o Supports all virtual machines, regardless of operating system or underlying hardware.
o Easy to set up, enabled and disabled per VM.
· Work process:
o Monitors all physical hosts and detects three types of failures: a host stops working, is isolated from the network, and loses network connectivity to a preferred host.
o The agent detects failures through “heartbeat signals” and automatically restarts VMs on other hosts when a failure occurs.
o Ensure that there are enough resources in the cluster to restart the VMs.
· Requirement:
o At least two ESX hosts are required.
o VM files must be on shared storage.
o Physical hosts can have different manufacturers and series of CPUs.
o All hosts can access common resources (shared storage, VM network).
o It is recommended to configure DNS information, DNS can resolve all hosts in the Cluster.
· Characteristics:
o Does not rely on vCenter to run, but must pass through vCenter when forming HA clusters.
o Brain Fracture” may occur.
o The service is interrupted briefly and is unplanned downtime.
o The virtual machine on the failed host will shut down and restart on another host.
VMware FT
· Function: Provides continuous availability of virtual machines with vLockstep technology for zero downtime and zero data loss.
· Advantage:
o Maximizes data center uptime.
o Eliminates the cost and complexity of traditional hardware or software clustering solutions.
o Ideal for business-critical applications.
· Work Process:
o Use vLockstep technology to ensure that the state of the primary and secondary VMs is always consistent.
o The primary VM captures all inputs and events and replays them on the secondary VM.
o The secondary VM executes the same sequence of instructions as the primary VM.
· Requirement:
o At least two ESX hosts are required, all ESX must be 4.0 or higher and have the same Build version.
o Server CPUs must be of the same series (AMD Barcelona+, Intel Penryn+).
o VT is enabled in BIOS, Hyperthreading and Power Management are disabled.
o Only 1 vCPU can be allocated per VM.
o A dedicated Gigabit network is required for FT.
o VM files must be on shared storage.
o VM configuration file must be version 7.
o Paravirtualization is not enabled for Guest OS.
· Characteristics:
o Avoid “cracked brain” scenarios.
o Zero downtime and zero data loss.
o FT-enabled VMs do not support Auto DRS, Snapshots, MS Cluster, Physical RDM Mapping, Virtual CD-ROM Connectivity, NPIV, Device Hotplugging.
Conclusion
VMware HA and VMware FT each have their own advantages and scenarios. HA is suitable for most applications, providing cost-effective high availability but with the possibility of transient service interruptions. ft is suitable for business-critical applications, providing zero downtime and zero data loss, but with more stringent requirements for hardware and configurations. Choosing the right solution depends on the specific application requirements and budget.