When VMware ESXi hosts face memory pressure, the balloon driver (vmmemctl) reclaims memory from guest VMs by inflating a "balloon" inside the guest OS. This shows as inflated balloon memory in vSphere metrics while reducing guest active memory. While this helps with memory management, the ballooned memory doesn't automatically release when new physical RAM becomes available.

You can detect ballooned VMs through these methods:

# PowerCLI example to list VMs with ballooned memory
Get-VM | Where-Object {$_.ExtensionData.Runtime.Memory.BalloonedMemory -gt 0} | 
Select-Object Name, @{N="BalloonedMB";E={$_.ExtensionData.Runtime.Memory.BalloonedMemory/1MB}}

Or via ESXTOP (real-time monitoring):

esxtop -b -n 1 -a > memory_stats.csv
# Look for "MCTL%" and "MCTLSZ" columns

While vMotion works, consider these alternatives:

# Method 1: Soft reboot (preferred)
Shutdown-VMGuest -VM "VM_Name" -Confirm:$false
Start-VM -VM "VM_Name"

# Method 2: Hot-add memory (if enabled)
$vm = Get-VM "VM_Name"
$spec = New-Object VMware.Vim.VirtualMachineConfigSpec
$spec.MemoryMB = $vm.MemoryMB + 1 # Add minimal amount
$vm.ExtensionData.ReconfigVM($spec)

# Method 3: API-driven balloon reset
$vm = Get-VM "VM_Name"
$vm.ExtensionData.ConsolidateVMDisks()

This PowerCLI script detects and handles ballooned VMs:

Connect-VIServer -Server vcenter.example.com

$thresholdMB = 256 # Minimum balloon size to trigger action
$balloonedVMs = Get-VM | Where-Object {
    $_.ExtensionData.Runtime.Memory.BalloonedMemory -gt ($thresholdMB * 1MB)
}

foreach ($vm in $balloonedVMs) {
    Write-Host "Processing $($vm.Name) with $($vm.ExtensionData.Runtime.Memory.BalloonedMemory/1MB)MB ballooned"
    
    try {
        # Attempt soft reset first
        Restart-VMGuest -VM $vm -Confirm:$false -ErrorAction Stop
        Start-Sleep -Seconds 30
    }
    catch {
        # Fallback to memory adjustment
        $spec = New-Object VMware.Vim.VirtualMachineConfigSpec
        $spec.MemoryMB = $vm.MemoryMB + 1
        $vm.ExtensionData.ReconfigVM($spec)
    }
    
    # Verify resolution
    $updatedBalloon = (Get-VM $vm.Name).ExtensionData.Runtime.Memory.BalloonedMemory
    Write-Host "Post-action balloon: $($updatedBalloon/1MB)MB"
}

• Configure DRS memory thresholds more aggressively
• Implement regular memory reclamation checks
• Consider setting memory reservations for critical VMs
• Monitor with vRealize Operations or similar tools

When working with VMware virtualization, memory ballooning is both a blessing and a curse. While it helps optimize memory usage across hosts, it can leave virtual machines in a "ballooned" state even after physical RAM becomes available. Let's explore effective ways to identify and resolve this situation.

You'll want to check these metrics programmatically:

# PowerCLI example to detect ballooned VMs
Get-VM | Where-Object {$_.ExtensionData.Guest.MemoryUsage -gt $_.MemoryMB} | 
Select-Object Name, MemoryMB, 
@{N="GuestMemoryUsage";E={$_.ExtensionData.Guest.MemoryUsage}},
@{N="Ballooned";E={($_.ExtensionData.Guest.MemoryUsage - $_.MemoryMB) / 1MB}}

Key indicators of ballooning:

• Guest memory usage exceeds configured memory (MemoryMB)
• High memory balloon size in performance metrics
• VMware Tools reporting inflated memory pressure

Besides vMotion, these techniques can help:

1. VM Reboot: Simple but disruptive
2. VMware Tools Restart: service vmware-tools restart
3. Hot-Add Adjustment: Temporarily increase then decrease memory allocation

For large environments, consider this Python script using pyVmomi:

from pyVmomi import vim
from pyVim.connect import SmartConnectNoSSL

def release_ballooned_vms(host, user, pwd):
    si = SmartConnectNoSSL(host=host, user=user, pwd=pwd)
    content = si.RetrieveContent()
    
    for vm in content.viewManager.CreateContainerView(
        content.rootFolder, [vim.VirtualMachine], True).view:
        
        if vm.runtime.powerState == vim.VirtualMachinePowerState.poweredOn:
            if vm.summary.quickStats.balloonedMemory > 0:
                print(f"Found ballooned VM: {vm.name}")
                # Trigger memory hot-add cycle
                spec = vim.vm.ConfigSpec()
                spec.memoryHotAddEnabled = True
                spec.memoryMB = vm.config.hardware.memoryMB + 1
                task = vm.ReconfigVM_Task(spec)
                WaitForTask(task)
                
                # Revert change
                spec.memoryMB = vm.config.hardware.memoryMB
                task = vm.ReconfigVM_Task(spec)
                WaitForTask(task)
                print(f"Memory released for {vm.name}")

Configuration tweaks to consider:

• Set Mem.AllocGuestLargePage=0 in VMX file
• Adjust DRS memory threshold settings
• Monitor and maintain adequate host memory headroom

For stubborn cases, here's a PowerCLI snippet to automate vMotion:

$targetHost = Get-VMHost -Name "target.esxi.host"
Get-VM | Where-Object {
    $_.ExtensionData.Guest.MemoryUsage -gt $_.MemoryMB
} | Move-VM -Destination $targetHost -Confirm:$false

Implement proactive monitoring with these approaches:

• vCenter Alarms for balloon driver activity
• Regular checks via vRealize Operations Manager
• Custom scripts running against vSphere API