vSAN availability technologies are designed to ensure data resilience and minimize downtime in the event of failures. These technologies work in tandem with VMware vSphere HA and the storage policy-based management (SPBM) framework to maintain the integrity of data and the availability of virtual machines. Understanding how vSAN handles failures at various levels is critical to maintaining a highly available environment.

vSAN achieves data availability by distributing data components across multiple hosts and fault domains based on policies. The most commonly used policy is failures to tolerate. This defines the number of host, disk, or fault domain failures a virtual machine object can withstand without data loss. For example, a RAID-1 mirror with one failure to tolerate (FTT=1) stores two copies of data on separate hosts. If one host fails, the other retains availability.

Beyond mirroring, vSAN also supports erasure coding with RAID-5 and RAID-6 configurations. RAID-5 supports one failure while RAID-6 tolerates two. These configurations offer space efficiency but require more hosts to satisfy policy requirements. Erasure coding is ideal for capacity-focused workloads that can tolerate slightly higher write latencies compared to mirroring.

One of the key availability mechanisms is vSAN’s ability to detect and respond to failures. When a component becomes inaccessible, vSAN determines whether the failure is transient or permanent. It uses a time-based mechanism to wait before rebuilding data, preventing unnecessary resyncs due to brief outages. The default delay is 60 minutes, after which a repair operation may commence if the component remains unavailable.

In addition to failure handling, vSAN includes automatic rebalancing features. When disk space across the cluster becomes uneven or after repairs, vSAN may redistribute components to optimize performance and avoid hotspots. This helps ensure balanced use of storage resources and sustained performance.

Witness components play an important role in maintaining quorum during failures. These are small metadata objects that participate in cluster decisions. For example, in a 2-node configuration, a witness resides on a separate host or appliance to act as a tie-breaker. This ensures that split-brain scenarios are avoided, and availability decisions are made accurately.

vSAN also incorporates features to protect against storage device failures. It can mark devices as degraded or failed and migrate components as needed. When a disk exhibits signs of wear or IO errors, vSAN initiates evacuation processes and alerts administrators via health checks and vCenter alarms.

Stretched cluster configurations allow for availability across two sites with a third witness site. Each site has its own fault domain, and vSAN ensures synchronous writes between them. In the event of a site failure, vSAN maintains availability by failing over to the other site. The witness in a third site helps determine which site should remain active, ensuring consistency and preventing data corruption.

Maintenance mode operations are also availability-aware. vSAN supports three modes: ensure accessibility, evacuate all data, and no data migration. The chosen mode affects whether VMs remain accessible during host maintenance and how data is protected. For example, ensure accessibility keeps data available but may reduce resilience until the host returns. Evacuate all data fully preserves availability by migrating components off the host in advance.

Proactive monitoring and alerting are critical to vSAN availability. Skyline Health checks for cluster, network, and hardware issues, while vCenter provides event logs and alerts for deeper investigation. Administrators can define alarms for capacity thresholds, degraded hardware, and other risk indicators to prevent outages.

In summary, vSAN offers a comprehensive set of availability technologies that span hardware failure detection, policy-driven resilience, automated repair and rebalancing, and integration with vSphere HA. These mechanisms ensure that virtualized workloads remain protected, resilient, and highly available, even in the face of component or site failures.

Troubleshooting vSAN performance requires a structured approach that considers the various components involved in a vSAN cluster. Performance issues can originate from compute, network, or storage layers, and identifying the root cause demands visibility into all three. Administrators should begin with clear problem definitions. Determine whether the issue is affecting a single VM, a set of workloads, or the entire cluster. It’s important to assess whether the issue is read or write related, and whether it is consistent or intermittent. These distinctions help narrow down the scope and focus the investigation.

vSAN Health and Skyline Health provide the first layer of diagnostics. These tools can indicate common misconfigurations, hardware issues, and network latency. Health checks should be reviewed for signs of contention, failed components, or cluster imbalance. Next, use vSAN Performance Service to gather metrics on IOPS, latency, and throughput at various levels including the cluster, disk group, and object layers. This visibility helps identify hotspots or bottlenecks that may not be immediately apparent.

Key metrics to analyze include write buffer usage, backend throughput, and resync activity. Elevated resync traffic from recent host failures or policy changes can reduce available bandwidth for regular I/O. Administrators should examine whether the congestion is due to background operations such as data rebuilds, rebalancing, or deduplication tasks. Disk group saturation, especially when cache drives are full or underperforming, is another common cause of elevated latency.

Network troubleshooting is essential. Check for dropped packets, high retransmissions, or latency spikes. vSAN is sensitive to network performance, and even minor disruptions can lead to delays in data replication or acknowledgments. Confirm that network hardware supports adequate throughput and low latency. Ensure all vSAN VMkernel interfaces are properly configured, with consistent MTU settings and failover policies.

Another important area to investigate is workload behavior. Some performance issues are tied to application characteristics rather than infrastructure faults. Identify whether the workload is generating large block writes, unaligned I/O, or excessive metadata operations. Test whether performance improves when running on alternative hardware or in a different vSAN cluster. This can help isolate whether the issue is systemic or localized.

Where possible, leverage performance graphs in vCenter, esxtop, or vSAN Observer for deeper analysis. Esxtop can be used to monitor CPU, memory, and disk contention in real time. Look for signs such as high device latency (DAVG), queue latency (QAVG), or kernel latency (KAVG). vSAN Observer can display the internal behavior of vSAN such as component ownership and object layout, giving insights into imbalance or misdistribution of data.

If a performance problem remains unresolved, consider collecting support bundles and engaging VMware GSS. Include a clear problem statement, the specific time range of impact, and any changes made in the environment that may have contributed. VMware recommends enabling advanced logging options before recreating the issue to capture sufficient detail.

Proactive steps can also prevent performance issues. Keep firmware and drivers up to date, validate hardware compatibility using the VMware Compatibility Guide, and avoid unnecessary policy changes during peak workloads. Regularly review capacity usage and aim to maintain at least 30% free space in vSAN to allow room for internal operations.

By combining structured analysis, proper tooling, and best practices, administrators can identify and resolve vSAN performance issues efficiently and minimize downtime across critical workloads.

vSAN File Services in VMware Cloud Foundation 9.0 introduces a powerful and streamlined way for administrators to provide file sharing capabilities directly from within the hypervisor layer. Whether serving SMB shares to Windows clients or NFS exports to Linux systems and cloud-native applications, vSAN File Services eliminates the need for traditional filers or separate virtual appliances. Its integration with vSphere makes deployment and ongoing administration simple, with configuration and management fully accessible through the vSphere Client UI.

This built-in service supports up to 500 file shares per cluster, with a limit of 100 SMB shares for Windows environments. Shares are intelligently distributed across the cluster using vSAN’s Cluster-Level Object Manager, and a dedicated protocol services layer ensures fair access and automatic load balancing. vSAN File Services supports Kerberos authentication for both NFS and SMB protocols, enhancing security and integration with enterprise environments.

Mounting shares is simplified through guided syntax in the UI, providing administrators with exact commands for mounting in Linux or connecting in Windows. This feature accounts for protocol version differences, including NFS v3 and NFS v4.1, and handles the appropriate redirection for optimal access.

vSAN File Services supports multiple deployment models, including hyperconverged clusters, disaggregated storage clusters, stretched clusters, and 2-node clusters. This flexibility makes it suitable for everything from core data centers to edge sites. Administrators can configure placement policies to ensure optimal site affinity, and services are automatically balanced to maintain performance and availability.

From a management perspective, everything is handled centrally via vCenter. Administrators can adjust storage policies, set quotas, configure access controls, and monitor usage. Integrated health checks appear in Skyline Health, covering file server availability, infrastructure health, and share status. Performance metrics such as IOPS, latency, and throughput are provided per share, alongside capacity usage statistics.

Security and governance features include quota enforcement and Access Based Enumeration, which hides files and folders users do not have permission to access. These features help reduce data exposure and support compliance goals.

Architecturally, vSAN File Services runs protocol services as stateless containers within agent VMs on each host. These containers handle I/O presentation for NFS or SMB shares but do not store data. Instead, the underlying vSAN Virtual Distributed File System handles data placement and storage, using vSAN objects to represent shares and apply policies for resilience and availability.

The system uses a zero-copy data path to minimize latency and reduce processing overhead. Failover mechanisms automatically reinstantiate containers on healthy hosts if needed, and containers are rebalanced every 30 minutes based on the number of shares served.

Scaling is straightforward. Adding hosts increases both capacity and share distribution, while growing share size triggers automatic creation of additional backing objects. This allows vSAN File Services to scale up or out depending on workload requirements.

Key considerations include reserving IP addresses for containers, ensuring proper DNS setup, and selecting either NFS or SMB per share. vSAN File Services does not support presenting NFS datastores to ESXi for VM storage, and snapshot capabilities are only available via API. Replication must be performed using external tools such as rsync or Robocopy.

vSAN File Services is a modern, hypervisor-integrated solution for providing enterprise-grade file shares across a wide range of deployment scenarios. It reduces complexity, improves manageability, and offers flexible performance and capacity benefits without the cost and overhead of separate file servers or appliances. For organizations already using vSAN, enabling File Services can simplify infrastructure and consolidate storage services into a single platform.

As data volumes continue to grow, space efficiency becomes a key concern for modern IT infrastructures. With the release of VMware Cloud Foundation 9.0, organizations can take advantage of new capabilities in vSAN to significantly optimize storage consumption without compromising performance.

In this article, we explore the opportunistic and deterministic space efficiency features built into vSAN, comparing the capabilities of the Original Storage Architecture (OSA) and the newer Express Storage Architecture (ESA).

Opportunistic features deliver savings based on data compressibility and structure, but results may vary. Key capabilities include:

Compression (ESA): In ESA, compression happens immediately at the top of the vSAN stack, before data is written to disk or transmitted across the network. This drastically reduces CPU and network utilization while improving performance—especially in stretched clusters.

Global Deduplication (ESA): Unlike OSA, where deduplication is disk group-bound, ESA enables cluster-wide deduplication with adaptive throttling. Deduplication is performed post-write and prioritizes cold data, minimizing performance impact.

Deduplication & Compression (OSA): In OSA, deduplication and compression are performed during destaging, which may degrade performance depending on the capacity tier. It’s a viable option for legacy environments but introduces latency in high-throughput workloads.

Compression-Only Mode (OSA): Introduced in vSAN 7 U1, this mode offers a middle ground—providing space savings without the overhead of deduplication. It’s particularly beneficial for performance-sensitive environments using modern flash storage.

These features guarantee capacity savings by using RAID-level redundancy instead of simple mirroring.

RAID-5/6 (ESA): With ESA, RAID-5 and RAID-6 deliver deterministic space efficiency without performance penalties. For instance, RAID-5 (4+1) consumes just 1.25x the data footprint, making it ideal for clusters with 6+ nodes.

RAID-5/6 (OSA): OSA uses a 3+1 or 4+2 data placement strategy. While this offers a significant reduction in capacity consumption compared to RAID-1, it comes at the cost of higher CPU, network, and I/O overhead—especially under high write loads.

Additional vSAN Space Saving Tools:

• Thin Provisioning: Efficient allocation of disk capacity on demand.

• TRIM/UNMAP: Reclaims unused space after guest OS deletions.

• Storage Policies: Fine-tuned controls for per-object resiliency and efficiency.

Recommendations:

Choose ESA whenever possible – It delivers superior space savings with no performance trade-offs.

Use Compression-only (OSA) for performance-sensitive workloads on legacy hardware.

Apply RAID-5/6 erasure coding in ESA to reduce capacity usage while maintaining high resilience.

Monitor space savings via vCenter Capacity View, and stay current with the latest vSAN releases to benefit from performance and efficiency enhancements.

With vSAN in VMware Cloud Foundation 9, organizations can confidently strike a balance between performance, resilience, and capacity optimization. Whether you’re modernizing with ESA or managing legacy OSA clusters, understanding and applying the right space efficiency techniques is key to maximizing your investment.

For hands-on workshops or custom vSAN training sessions, feel free to get in touch.