IT infrastructure / Virtualization · Guide · ~9 min

Server high availability — keeping IT infrastructure running

Alterkom – Technology Team. HA clusters, redundancy, RPO/RTO and Disaster Recovery — without confusing HA with backup.

A single server failure does not have to stop the business. High Availability (HA) limits the impact of hardware and service outages — but it takes more than buying two servers: architecture, operations and regular failover tests matter.

What is High Availability?

HA designs IT systems to reduce downtime using redundant resources, monitoring and failover. A virtualization cluster can restart a VM on another host after a failure — planned live migration and unplanned host failure behave differently.

Availability percentages

Availability	Approx. max annual downtime
99%	about 3 days 15 hours
99.9%	about 8 hours 46 minutes
99.99%	about 52 minutes
99.999%	about 5 minutes

Infrastructure redundancy alone does not guarantee an SLA. Platforms such as VMware, Hyper-V and Proxmox VE each offer HA features — choose based on apps, cost and team skills.

HA vs Disaster Recovery

HA limits local failures; DR recovers after site-level incidents. Neither replaces backup. Define RPO and RTO from business needs, then design clusters, storage and networks accordingly.

Alterkom designs and delivers high-availability infrastructure, virtualization clusters, backup and Disaster Recovery.

99.9% vs 99.99% availability

Availability tiers differ meaningfully in annual downtime. Infrastructure redundancy alone does not guarantee an SLA.

Availability	Approx. max annual downtime
99%	about 3 days 15 hours
99.9%	about 8 hours 46 minutes
99.95%	about 4 hours 23 minutes
99.99%	about 52 minutes
99.999%	about 5 minutes

Core HA architecture elements

Server, storage, network and power redundancy plus monitoring, quorum, fencing and failover tests.

HA cluster architecture

Three hosts, redundant networks, storage, quorum and failover. HA only works when critical paths are not single points of failure.

IT infrastructure area

VMware, Hyper-V or Proxmox VE?

Each platform offers HA features. Choose based on applications, cost, skills and roadmap — there is no universal winner.

High Availability vs Disaster Recovery

HA limits local failures; DR recovers after site loss. Replication does not replace backup.

Storage area

RPO, RTO and common mistakes

Define RPO and RTO from business needs. Avoid single points of failure, missing quorum/fencing, untested failover and treating HA as a backup substitute.