In a vSAN environment, data is distributed across multiple hosts and disks for redundancy and fault tolerance. If some components are lost, vSAN employs various mechanisms to ensure data integrity and availability:

1. Automatic Component Repair:
   • vSAN automatically repairs missing or degraded components when possible.
   • When a component (e.g., a disk or a host) fails, vSAN automatically starts rebuilding the missing components using available replicas.
2. Fault Domains:
   • Fault domains are logical groupings of hosts and disks that provide data resiliency against larger failures, such as an entire rack or network segment going offline.
   • By defining fault domains properly, vSAN ensures that data replicas are distributed across different failure domains.
3. Policy-Based Management:
   • Use vSAN storage policies to specify the level of redundancy and performance required for your VMs.
   • Policies dictate how many replicas to create, where to place them, and what to do in case of failures.
4. Health Checks and Alerts:
   • Regularly monitor the vSAN cluster’s health using vSAN Health Check and other monitoring tools.
   • Address any alerts promptly to prevent further issues.
5. Recovery from Complete Host Failure:
   • In the event of a complete host failure, VMs and their data remain accessible if enough replicas exist on surviving hosts.
   • Replace the failed host and vSAN automatically resyncs the data back to the new host.

Automatic Component Repair in vSAN is a critical feature that helps maintain data integrity and availability in case of component failures. When a component (such as a disk, a cache drive, or an entire host) fails, vSAN automatically initiates the process of rebuilding the affected components to restore data redundancy. Let’s understand how Automatic Component Repair works in vSAN with some examples:

Example 1: Disk Component Failure

1. Initial Configuration:
   • Let’s assume we have a vSAN cluster with three hosts (Host A, Host B, and Host C) and a single VM with RAID-1 (Mirroring) vSAN storage policy, which means each data object has two replicas (copies).
2. Normal Operation:
   • The VM’s data is distributed across the three hosts, with two replicas on different hosts to ensure redundancy.
3. Disk Failure:
   • Suppose a disk on Host A fails, and it contains one of the replicas of the VM’s data.
4. Automatic Component Repair:
   • As soon as the disk failure is detected, vSAN will automatically trigger a process to rebuild the lost replica.
   • The surviving replica on Host B will be used as the source to rebuild the missing replica on another healthy disk within the cluster, which could be on Host A or Host C.
5. Recovery Completion:
   • Once the new replica is created on a different disk within the cluster, the VM’s data is fully protected again with two replicas.

Example 2: Host Failure

1. Initial Configuration:
   • Similar to the previous example, we have a vSAN cluster with three hosts (Host A, Host B, and Host C) and a VM with RAID-1 vSAN storage policy.
2. Normal Operation:
   • The VM’s data is distributed across the three hosts with two replicas for redundancy.
3. Host Failure:
   • Let’s say Host B experiences a complete failure and goes offline.
4. Automatic Component Repair:
   • As soon as vSAN detects the host failure, it will trigger a process to rebuild the lost replicas that were residing on Host B.
   • The replicas that were on Host B will be recreated on available disks in the cluster, such as on Host A or Host C.
5. Recovery Completion:
   • Once the new replicas are created on the surviving hosts, the VM’s data is again fully protected with two replicas.

Automatic Component Repair ensures that vSAN maintains the desired level of data redundancy specified in the storage policy. The process of rebuilding components may take some time, depending on the size of the data and the available resources in the cluster. During the repair process, vSAN continues to operate in a degraded state, but data accessibility is maintained as long as the remaining replicas are available.

It’s important to note that vSAN Health Checks and monitoring tools can provide insights into the status of the cluster and any ongoing repair activities.

These tools assist in identifying potential issues, optimizing performance, and ensuring data integrity. Here are some essential vSAN monitoring tools:

1. vSAN Health Check:
   • The vSAN Health Check is an integrated tool within the vSphere Web Client that provides a comprehensive health assessment of the vSAN environment.
   • It checks for potential issues, misconfigurations, or capacity problems and offers remediation steps.
   • You can access the vSAN Health Check from the vSphere Web Client by navigating to “Monitor” > “vSAN” > “Health.”
2. Performance Service:
   • The vSAN Performance Service provides real-time performance metrics and statistics for vSAN clusters and individual VMs.
   • It allows you to monitor metrics like throughput, IOPS, latency, and other performance-related information.
   • You can access the vSAN Performance Service from the vSphere Web Client by navigating to “Monitor” > “vSAN” > “Performance.”
3. vRealize Operations Manager (vROps):
   • vRealize Operations Manager is an advanced monitoring and analytics tool from VMware that provides comprehensive monitoring and capacity planning capabilities for vSAN environments.
   • It offers in-depth insights into performance, capacity, and health of the entire vSAN infrastructure.
   • vROps also provides customizable dashboards, alerting, and reporting features.
   • vRealize Operations Manager can be integrated with vCenter Server to get the vSAN-specific analytics and monitoring features.
4. esxcli Commands:
   • ESXi hosts in the vSAN cluster can be monitored using various esxcli commands.
   • For example, you can use “esxcli vsan cluster get” to view cluster information, “esxcli vsan storage list” to check disk health, and “esxcli vsan debug perf get” to retrieve performance-related data.
5. vSAN Observer:
   • The vSAN Observer is a tool that provides advanced performance monitoring and troubleshooting capabilities for vSAN clusters.
   • It collects detailed performance metrics and presents them in a user-friendly format.
   • The vSAN Observer can be accessed from an SSH session to the ESXi hosts, and you can run “vsan.observer” to initiate the collection.
6. VMware Skyline Health Diagnostics for vSAN:
   • VMware Skyline is a proactive support technology that automatically analyzes vSAN environments for potential issues and sends recommendations to VMware Support.
   • It provides insights into vSAN configuration, hardware compatibility, and other relevant information to improve the health of the environment.

I personally use vSAN Observer a lot in my daily VSAN checks.

Accessing VSAN Observer: To use VSAN Observer, you need to access the ESXi host via an SSH session. SSH should be enabled on the ESXi host to use this tool. You can use tools like PuTTY (Windows) or the Terminal (macOS/Linux) to connect to the ESXi host.

1. Start VSAN Observer: To initiate the VSAN Observer, run the following command on the ESXi host:

vsan.observer

2. View VSAN Observer Output: After running the command, VSAN Observer starts collecting performance statistics and presents an output similar to the top command in a continuous mode. It updates the performance statistics at regular intervals.
3. Navigating VSAN Observer: The VSAN Observer output consists of multiple sections, each displaying different performance metrics related to vSAN.

• General Overview: The initial section provides a general overview of the vSAN cluster, including health status and disk capacity utilization.
• Network: This section displays network-related performance metrics, such as throughput, packets, and errors.
• Disk Groups: Information about each disk group in the cluster, including read and write latency, cache hit rate, and IOPS.
• SSD: Performance statistics for the SSDs used in the disk groups.
• HDD: Performance statistics for the HDDs used in the disk groups.
• Virtual Machines: Performance metrics for individual VMs using vSAN storage.

4. Navigating VSAN Observer Output: Use the arrow keys and other keyboard shortcuts to navigate through the different sections and information displayed by VSAN Observer.
5. Exit VSAN Observer: To exit VSAN Observer, press “Ctrl + C” in the SSH session.

Example: Using VSAN Observer to Monitor Disk Group Performance:

Let’s use VSAN Observer to monitor the performance of disk groups in a vSAN cluster.

1. Access the ESXi host via SSH.
2. Start VSAN Observer by running the following command:

vsan.observer

3. Navigate to the “Disk Groups” section using the arrow keys.
4. Observe the performance metrics for each disk group, such as read and write latency, cache hit rate, and IOPS.
5. Monitor the output for any anomalies or performance bottlenecks in the disk groups.
6. To exit VSAN Observer, press “Ctrl + C” in the SSH session.