Automating vSAN Policy Application: Building the Dashboard 2 of 5

Series

1, 2, 3, 4, 5

Problem

• Difficulty in determining appropriate vSAN policies based on VM I/O characteristics
• Lack of automated metrics to assess read/write percentages for virtual disks
• Challenges in dynamically selecting optimal RAID policies for vSAN
• Need for quantifiable data to make informed storage policy decisions

Troubleshooting

When attempting to automate vSAN policy decisions, several challenges arise:

1. Accurately measuring write vs. read operations for VMs
2. Determining appropriate thresholds for policy changes
3. Combining multiple factors (disk space, I/O operations) for RAID policy decisions
4. Integrating custom metrics into existing vSphere environments

Solution

Create Super Metrics in vSphere to calculate key I/O characteristics for automated policy decisions:

1. vDisk Write Percentage Super Metric

# Navigate to: Configure -> Super Metrics -> Add
$vDiskWriteMetric = @{
    Name = "vDisk Write Percentage"
    Description = "vDisk Write Percentage"
    ObjectTypes = "Virtual Machine"
    Formula = @"
(max({‌This Resource: ‌virtualDisk:Aggregate of all instances|numberWriteAveraged_average})
/
max({‌This Resource: ‌virtualDisk:Aggregate of all instances|commandsAveraged_average}))
* 100
"@
}

# Add the Super Metric using vSphere API or UI

This metric calculates the percentage of write operations relative to total I/O commands for a virtual disk.

2. vDisk Read Percentage Super Metric

# Navigate to: Configure -> Super Metrics -> Add
$vDiskReadMetric = @{
    Name = "vDisk Read Percentage"
    Description = "vDisk Read Percentage"
    ObjectTypes = "Virtual Machine"
    Formula = @"
(max({‌This Resource: ‌virtualDisk:Aggregate of all instances|numberReadAveraged_average})
/
max({‌This Resource: ‌virtualDisk:Aggregate of all instances|commandsAveraged_average}))
* 100
"@
}

# Add the Super Metric using vSphere API or UI

This metric calculates the percentage of read operations relative to total I/O commands for a virtual disk.

3. vSAN RAID Policy Super Metric

# Navigate to: Configure -> Super Metrics -> Add
$vSANRAIDPolicyMetric = @{
    Name = "vSAN RAID Policy"
    Description = "vSAN RAID Policy"
    ObjectTypes = "Virtual Machine"
    Formula = @"
count({‌This Resource: ‌diskspace|used, depth=1, where= ($value >= 1000)})
&&
count({‌This Resource: ‌virtualDisk:Aggregate of all instances|numberWriteAveraged_average, depth=1, where= ($value <= 250)})
&&
count({‌This Resource: ‌Super Metrics|vDisk Read Percentage, depth=1, where= ($value >= 30)})
? 5: 1
"@
}

# Add the Super Metric using vSphere API or UI

This metric combines disk space usage, write operations, and read percentage to determine the appropriate RAID policy for vSAN.

Implementation Steps

1. Access the vSphere Client
2. Navigate to the Super Metrics configuration section
3. Add each Super Metric using the provided formulas
4. Set appropriate policies for each metric (default or custom)
5. Note down the ID of the “vSAN RAID Policy” metric for script integration

Integration with Automation Script

• Import the created Super Metrics into your automation script
• If import issues occur, manually create the metrics
• Update your PowerShell script with the ID of the “vSAN RAID Policy” metric

Benefits

• Provides quantifiable data on VM I/O characteristics
• Enables dynamic, data-driven vSAN policy decisions
• Automates the process of selecting optimal RAID policies
• Enhances overall storage performance and efficiency in vSAN environments

In the next part of this series, we’ll explore how to leverage these Super Metrics in our automation script to apply optimal vSAN policies.