optimize-hypervisorvdas.ps1

<#
    .SYNOPSIS
    Reviews and evenly distributes VDA's within a Citrix Hypervisor pool.
    .DESCRIPTION
    Reviews and evenly distributes VDA's within a Citrix Hypervisor pool.
    .PARAMETER XenServer_poolmaster
    Mandatory string parameter. IP of the Citrix Hypervisor pool master to optimize.
    .PARAMETER XenServer_networkname
    Mandatory string parameter. Network name of the Citrix Hpervisor pool's management network
    .PARAMETER XenServer_SRName
    Mandatory string parameter. Storage Repository name that stores the vDisks of the Citrix Hpervisor pool
    .EXAMPLE
    optimize-hypervisorvdas.ps1 -xenserver_poolmaster "127.0.0.1" -xenserver_networkname "HypervisorMGMTNet" -XenServer_SRName "HypervisorSR" -verbose

    Counts the total VMs in the 127.0.0.1 Hypervisor pool and evently distributes them with additional console feedback.
    .INPUTS
    None
    .OUTPUTS
    None
    .NOTES
    NAME: optimize-hypervisorvdas.ps1
    VERSION: 1.0.2
    CHANGE LOG - Version - When - What - Who
    0.0.1 - 12/06/2022 - Initial script - Alain Assaf
    0.0.2 - 12/22/2022 - Added hypervisor connection/disconnection functions - Alain Assaf
    0.0.3 - 12/28/2022 - Added new functions get-hypNetwork & get-hypSR - Alain Assaf
    0.0.4 - 12/28/2022 - Added params XenServer_networkname & XenServer_SRName - Alain Assaf
    0.0.5 - 12/29/2022 - Added change to get-ctxHypVMTable function - Alain Assaf
    0.0.6 - 12/30/2022 - Added additional functions related to migration - Alain Assaf
    0.0.7 - 2/14/2023 - Added new link. Updates function calls for new params - Alain Assaf
    0.0.8 - 2/23/2023 - Make sure all existing XenServer connected are stopped before script starts - Alain Assaf
    1.0.0 - 3/06/2023 - Removed commented lines and converted write-host to write-verbose - Alain Assaf
    1.0.1 - 3/06/2023 - Updated Requries statement - Alain Assaf
    1.0.2 - 3/07/2023 - Updated help - Alain Assaf
    AUTHOR: Alain Assaf
    LASTEDIT: March 07, 2023
    .LINK
    https://jordantheitguy.com/2019/06/24/how-to-powershell-progress-bars/
    https://discussions.citrix.com/topic/415099-invoke-xenvm-xenaction-migratesend/page/2/
    https://discussions.citrix.com/topic/399153-vm-migration-to-homeserver-via-powershell/
    https://devblogs.microsoft.com/scripting/rounding-numberspowershell-style/
    http: //www.linkedin.com/in/alainassaf/
#>
[CmdletBinding()]
Param(
    [parameter(Mandatory)]
    [string]$XenServer_poolmaster,

    [parameter(Mandatory)]
    [string]$XenServer_networkname,

    [parameter(Mandatory)]
    [string]$XenServer_SRName
)

#region functions
function get-scriptCredential {
    param (
        [Parameter(Mandatory = $true)]
        [String]$userName,

        [Parameter(Mandatory = $true)]
        [String]$PassPath
    )

    # If Password file does not exist, create it
    if ((Test-Path -Path $PassPath) -eq $False) {
        (Get-Credential -Message "ENTER CREDENTIALS" -UserName $userName).Password | ConvertFrom-SecureString | Out-File $PassPath
    }

    $cred_password = Get-Content $PassPath | ConvertTo-SecureString
    $credential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $userName, $cred_password
    Return $credential
}

Function Get-MySnapin {
    <#
    .SYNOPSIS
    Checks for a PowerShell Snapin(s) and imports it if available, otherwise it will display a warning and exit.
    .DESCRIPTION
    Checks for a PowerShell Snapin(s) and imports it if available, otherwise it will display a warning and exit.
    .PARAMETER snapins
    Required parameter. List of PSSnapins separated by commas.
    .INPUTS
    None
    .OUTPUTS
    None
    .EXAMPLE
    PS> get-MySnapin PSSNAPIN
    Checks system for installed PSSNAPIN and imports it if available.
    .LINK
    http://www.linkedin.com/in/alainassaf/
    https://github.com/alainassaf/get-mysnapin
    .NOTES
    NAME        :  Get-MySnapin
    VERSION     :  1.01
    CHANGE LOG - Version - When - What - Who
    1.00 - 02/13/2017 - Initial script - Alain Assaf
    1.01 - 11/7/2017 - Added try/catch - Alain Assaf
    LAST UPDATED:  11/7/2017
    AUTHOR      :  Alain Assaf
#>
    Param([string]$snapins)
    $ErrorActionPreference = 'silentlycontinue'
    foreach ($snap in $snapins.Split(",")) {
        if (-not(Get-PSSnapin -Name $snap)) {
            if (Get-PSSnapin -Registered | Where-Object { $_.name -like $snap }) {
                try {
                    Add-PSSnapin -Name $snap
                    $true
                } catch {
                    Write-Warning "$snap PowerShell Cmdlet not available."
                    Write-Warning "Please run this script from a system with the $snap PowerShell Cmdlet installed."
                    exit 1
                }
            }
        }
    }
}

function connect-ctxhyp {
    <#
    .SYNOPSIS
    Connects to Citrix Hypervisor. Returns object with XenServer Connection
    .PARAMETER poolMaster
    Required string parameter. IP of the Hypervisor poolmaster.
    .PARAMETER hypCreds
    Required PSCredential parameter. Username and password PSCredentail object to authenticate to the Hypervisor.
    .INPUTS
    None
    .OUTPUTS
    XenAPI.Session
    .EXAMPLE
    PS> connect-ctxhyp -poolMaster "192.168.25.1" -hypCreds $credentials

    Connects Citrix Hypervisor at 192.168.25.1 using $credentials for authentication.
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  connect-ctxhyp
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/22/2022 - Initial script - Alain Assaf
    LAST UPDATED:  12/22/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    param (
        [Parameter(Mandatory)]
        [string]$poolMaster,

        [Parameter(Mandatory)]
        [System.Management.Automation.PSCredential]$hypCreds
    )
    Try {
        Connect-XenServer -Server $poolMaster -Creds $hypCreds -NoWarnNewCertificates -SetDefaultSession
        $hypSession = Get-XenSession
        return $hypSession
    } Catch [XenAPI.Failure] {
        Write-Warning "Failed to connect to [$poolMaster]"
        Exit 1
    }
}

function disconnect-ctxhyp {
    <#
    .SYNOPSIS
    Disconnect all open Citrix Hypervisor sessions.
    .INPUTS
    None
    .OUTPUTS
    None
    .EXAMPLE
    PS> disconnect-ctxhyp

    Disconnects and closes all open Citrix Hyperivsor sessions
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  disconnect-ctxhyp
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/22/2022 - Initial script - Alain Assaf
    LAST UPDATED:  12/22/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    param ()
    try {
        Get-XenSession | Disconnect-XenServer | Out-Null
    } catch {
        Write-Warning "Already disconnected from XenServer"
    }
}

function get-ctxHypVMTable {
    <#
    .SYNOPSIS
    Generates a table with the hypervisor host, uuid, and VM Count.
    .INPUTS
    XenAPI.Session
    .OUTPUTS
    PSCustomObject
    .EXAMPLE
    PS> get-ctxHypVMTable

    Generates a table with the hypervisor host, uuid, and VM Count for the current Citrix hypervisor session
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  get-ctxHypVMTable
    VERSION     :  1.0.2
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/22/2022 - Initial script - Alain Assaf
    1.0.1 - 12/29/2022 - Added write-progress to show progress - Alain Assaf
    1.0.2 - 2/14/2023 - Added Session param - Alain Assaf
    LAST UPDATED:  12/29/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    [CmdletBinding()]
    param (
        [Parameter()]
        [XenAPI.Session]$hypSession
    )

    $hypTable = @()
    [int]$hypCount = 1
    $hypHosts = Get-XenHost -SessionOpaqueRef $hypSession.opaque_ref | Sort-Object name_label
    foreach ($hypervisor in $hypHosts) {
        Write-Progress -Activity "Creating VM Table" -Status "Examing Host - $($hypervisor.Name_label) $hypCount of $($hypHosts.Count)"
        $row1 = $hypervisor.name_label
        $row2 = $hypervisor.uuid
        $row3 = ($hypervisor | Select-Object -ExpandProperty resident_VMs | ForEach-Object { (Get-XenVM -opaque_ref $_) | Where-Object { $_.is_control_domain -eq $false } }).count
        $hypTable += [PSCustomObject]@{HypervisorName = $row1; UUID = $row2; VMCount = $row3 }
        $hypCount++
    }

    return $hypTable
}

function get-ctxHypSource {
    <#
    .SYNOPSIS
    Returns a table of hypervisor hosts with more than the 'ideal' number of VMs.
    .INPUTS
    PSCustomObject
    .OUTPUTS
    PSCustomObject
    .EXAMPLE
    PS> get-ctxHypSource -idealNumberOfVMs 8 -hypTable $HyperVisorTable

    Returns a subset of items from $HypervisorTable with a VM count higher than 8
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  get-ctxHypSource
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/29/2022 - Initial script - Alain Assaf
    LAST UPDATED:  12/29/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [Int]$idealNumberOfVMs,
        [Parameter(Mandatory)]
        [PSCustomObject]$hypTable
    )

    $hypSourceTable = @()
    [int]$hypCount = 1
    foreach ($hypervisor in $hypTable) {
        Write-Progress -Activity "Creating Hypervisor Source Table" -Status "Examing Host - $($hypervisor.Name_label) $hypCount of $($hypTable.Count)"
        if ($hypervisor.VMCount -gt $idealNumberOfVMs) {
            $row1 = $hypervisor.HypervisorName
            $row2 = $hypervisor.uuid
            $row3 = $hypervisor.VMcount
            $hypSourceTable += [PSCustomObject]@{HypervisorName = $row1; UUID = $row2; VMCount = $row3 }
            $hypCount++
        }
    }

    return $hypSourceTable
}

function get-ctxHypDest {
    <#
    .SYNOPSIS
    Returns a table of hypervisor hosts with less than the 'ideal' number of VMs.
    .INPUTS
    PSCustomObject
    .OUTPUTS
    PSCustomObject
    .EXAMPLE
    PS> get-ctxHypDest -idealNumberOfVMs 8 -hypTable $HyperVisorTable

    Returns a subset of items from $HypervisorTable with a VM count less than 8
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  get-ctxHypDest
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/29/2022 - Initial script - Alain Assaf
    LAST UPDATED:  12/29/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [Int]$idealNumberOfVMs,
        [Parameter(Mandatory)]
        [PSCustomObject]$hypTable
    )

    $hypDestTable = @()
    [int]$hypCount = 1
    foreach ($hypervisor in $hypTable) {
        Write-Progress -Activity "Creating Hypervisor Destination Table" -Status "Examing Host - $($hypervisor.Name_label) $hypCount of $($hypTable.Count)"
        if ($hypervisor.VMCount -lt $idealNumberOfVMs) {
            $row1 = $hypervisor.HypervisorName
            $row2 = $hypervisor.uuid
            $row3 = $hypervisor.VMcount
            $hypDestTable += [PSCustomObject]@{HypervisorName = $row1; UUID = $row2; VMCount = $row3 }
            $hypCount++
        }
    }

    return $hypDestTable
}

function get-hypHost {
    <#
    .SYNOPSIS
    Returns a hypervisor host object
    .INPUTS
    None
    .OUTPUTS
    XenAPI.Host
    .EXAMPLE
    PS> get-hypHost -hostUUID "b671f78b-db28-4902-ad07-062c368fd8c2"

    Retrurns XenAPI.Host object with uuid b671f78b-db28-4902-ad07-062c368fd8c2
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  get-hypHost
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/23/2022 - Initial script - Alain Assaf
    LAST UPDATED:  12/23/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule

    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        $hostUUID
    )

    try {
        $hypHost = Get-XenHost -Uuid $hostUUID
        Return $hypHost
    } catch {
        Write-Warning "Could not find Hypervisor with uuid: [$hostUUID]"
        Exit 1
    }

}

function get-hypNetwork {
    <#
    .SYNOPSIS
    Returns a hypervisor network
    .INPUTS
    None
    .OUTPUTS
    XenAPI.Network
    .EXAMPLE
    PS> get-hypNetwork -xenNetName "PRODUCTION"

    Retrurns XenAPI.Network object with name_label'"PRODUCTION'
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  get-hypNetwork
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/28/2022 - Initial script - Alain Assaf
    LAST UPDATED:  12/28/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule

    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [String]$xenNetName
    )

    try {
        $hypNetwork = Get-XenNetwork -name_label $xenNetName
        Return $hypNetwork
    } catch {
        Write-Warning "Could not find Hypervisor network named: [$xenNetName]"
        Write-Warning "Closing Citrix Hypervisor connection"
        disconnect-ctxhyp
        Exit 1
    }

}

function get-hypSR {
    <#
    .SYNOPSIS
    Returns a hypervisor Storage Repository
    .INPUTS
    None
    .OUTPUTS
    XenAPI.Storage
    .EXAMPLE
    PS> get-hypSR xenSRName "VDA-SR"

    Retrurns XenAPI.Storage object with name_label 'VDA-SR'
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  get-hypSR
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 12/28/2022 - Initial script - Alain Assaf
    LAST UPDATED:  12/28/2022
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule

    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [String]$xenSRName
    )

    try {
        $hypSR = Get-XenSR -name_label $xenSRName
        Return $hypSR
    } catch {
        Write-Warning "Could not find Hypervisor Storage Repository named: [$xenSRName]"
        Write-Warning "Closing Citrix Hypervisor connection"
        disconnect-ctxhyp
        Exit 1
    }

}

function get-vmToMigrate {
    <#
    .SYNOPSIS
    Returns the first VM object from a hypervisor with its disks. This VM will be migrated off the hypervisor host.
    .PARAMETER hypTableRow
    Mandatory PSCustomObject of a hypTable row
    .PARAMETER vmSR
    Mandatory Storage Repository where migration VM disks reside
    .INPUTS
    PSCustomObject
    .OUTPUTS
    PSCustomObject
    .EXAMPLE
    PS> get-vmToMigrateName -hypTableRow $HypTableRow -vmSR $vmSR

    Queries hypervisor for VMs and returns first 1 to migrate with the VM's disks
    .LINK
    http://www.linkedin.com/in/alainassaf/
    .NOTES
    NAME        :  get-vmToMigrateName
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 1/26/2023 - Initial script - Alain Assaf
    LAST UPDATED:  1/26/2023
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [PSCustomObject]$hypTableRow,

        [Parameter(Mandatory)]
        $vmSR
    )
    $migrateHostVM = (Get-XenHost -Uuid $hypTableRow.uuid) | Select-Object -ExpandProperty resident_VMs | Select-Object -First 1
    $VMtoMove = Get-XenVM -opaque_ref $migrateHostVM

    ##VDI's should be resolved from $tmpVM.VBDs https://discussions.citrix.com/topic/415099-invoke-xenvm-xenaction-migratesend/page/2/
    $vdirefs = @()
    foreach ($itemvbd in $VMtoMove.VBDs) {
        $vbdvm = Get-XenVBD -opaque_ref $itemvbd.opaque_ref
        if ($vbdvm.type -eq "Disk") {
            $vdirefs += Get-XenVDI -opaque_ref $vbdvm.VDI.opaque_ref | ConvertTo-XenRef
        }
    }

    #Map disks to $vdimap to use in migrate tasks
    $vdimap = @{}
    foreach ($vdiref in $vdirefs) {
        $vdimap.Add([XenAPI.XenRef[XenAPI.VDI]]$vdiref, [XenAPI.XenRef[XenAPI.SR]]$vmSR);
    }

    $migrateVM = [PSCustomObject]@{vmToMigrate = $VMtoMove; vdiMap = $vdimap }

    Return $migrateVM
}

function get-destHyp {
    <#
    .SYNOPSIS
    Gets destination host to migrate a VM to
    .PARAMETER hypTableRow
    Mandatory PSCustomObject of a hypTable row
    .PARAMETER hypNet
    Mandatory [XenAPI.Network] that VM resides on
    .INPUTS
    PSCustomObject,XenAPI.Network
    .OUTPUTS
    PSCustomObject
    .EXAMPLE
    PS> get-destHyp -hypTableRow $HypTableRow -hypNet $HypervisorNetwork

    Returns a XenAPI.VM of the destination hypervisor
    .LINK
    http://www.linkedin.com/in/alainassaf/
    https://discussions.citrix.com/topic/415099-invoke-xenvm-xenaction-migratesend/page/2/
    .NOTES
    NAME        :  get-destHyp
    VERSION     :  1.0.0
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 1/27/2023 - Initial script - Alain Assaf
    LAST UPDATED:  1/27/2023
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [PSCustomObject]$hypTableRow,

        [Parameter(Mandatory)]
        [XenAPI.Network]$hypNet
    )

    $desthost = Get-hypHost -hostUUID $hypTableRow.uuid
    $VMdest = Invoke-XenHost -XenHost $desthost -XenAction migratereceive -network $hypNet -PassThru

    return $VMdest
}

function invoke-vmMigration {
    <#
    .SYNOPSIS
    Initates VM Migration
    .PARAMETER VMtoMigrate
    Mandatory XenAPI.VM parameter of VM to migrate
    .PARAMETER DestinationHost
    Mandatory object of the destination Hypervisor
    .PARAMETER VMVIFMap
    Mandatory object array of Migration VM's vifs
    .PARAMETER VMVDIMap
    Mandatory object array of Migration VM's disks
    .PARAMETER hpySession
    Mandatory XenAPI.Session object of the XenServer session where the migration will occur
    .INPUTS
    PSCustomObject,XenAPI.Network
    .OUTPUTS
    PSCustomObject
    .EXAMPLE
    PS> invoke-vmMigration -hypTableRow $HypTableRow -hypNet $HypervisorNetwork

    Starts migratio of
    .LINK
    http://www.linkedin.com/in/alainassaf/
    https://discussions.citrix.com/topic/415099-invoke-xenvm-xenaction-migratesend/page/2/
    .NOTES
    NAME        :  get-destHyp
    VERSION     :  1.0.2
    CHANGE LOG - Version - When - What - Who
    1.0.0 - 1/27/2023 - Initial script - Alain Assaf
    1.0.1 - 1/30/2023 - Added additional parameters - Alain Assaf
    1.0.2 - 2/14/2023 - Added VMVIFMap param - Alain Assaf
    LAST UPDATED:  2/14/2023
    AUTHOR      :  Alain Assaf
    #>
    #Requires -Version 4
    #Requires -Module XenServerPSModule
    [CmdletBinding()]
    param (
        [Parameter(Mandatory)]
        [XenAPI.VM]$VMtoMigrate,

        [Parameter(Mandatory)]
        $DestinationHost,

        [Parameter(Mandatory)]
        [AllowNull()]
        $VMVIFMap,

        [Parameter(Mandatory)]
        $VMVDIMap,

        [Parameter(Mandatory)]
        [XenAPI.Session]$hpySession
    )

    $xenMotionTask = Invoke-XenVM $VMtoMigrate -XenAction migratesend -live $true -dest $DestinationHost -VifMap $VMVIFMap -VdiMap $VMVDIMap -SessionOpaqueRef $hypSession.opaque_ref -BestEffort -Async -PassThru

    return $xenMotionTask
}

#endregion

#region variables
$datetime = Get-Date -Format "MM-dd-yyyy_HH-mm"
$Domain = (Get-ChildItem env:USERDNSDOMAIN).value
$ScriptRunner = (Get-ChildItem env:username).value
$compname = (Get-ChildItem env:COMPUTERNAME).value
$scriptName = $MyInvocation.MyCommand.Name
$scriptpath = $MyInvocation.MyCommand.Path
#$currentDir = Split-Path $MyInvocation.MyCommand.Path
#endregion

#region modules
# Import the Citrix Broker PowerShell module
Get-MySnapin Citrix.Broker.Admin.V2

# Import the XenServer Module
Get-MySnapin XenServerPowerShell
#endregion

#Remove any existing XenServer sessions
disconnect-ctxhyp

#Get XenServer Credential
Write-Verbose "Getting XenServer Credentials (for root user)..."
$XenServer_credential = get-scriptCredential -userName "root" -passpath "c:\temp\XenServer_pool.pwd"

#Connect to XenServer
$session = connect-ctxhyp -poolMaster "$XenServer_poolmaster" -hypCreds $XenServer_credential

#Get Pool Friendly name. Populate to match your environment
switch ($XenServer_poolmaster) {
    "127.0.0.1" { $xsn = "XS-Pool1"; break }
    "127.0.0.10" { $xsn = "XS-Pool2"; break }
    "127.0.0.20" { $xsn = "XS-Pool3"; break }
    "127.0.0.30" { $xsn = "XS-Pool4"; break }
    default { "UNKNOWN XENSERVER"; break }
}

#This network will be used for VM migration
$xennet = get-hypNetwork -xenNetName $XenServer_networkname
if ($null -eq $xennet) {
    Write-Warning "XenServer network [$XenServer_networkname] was not correct. Try another network name."
    disconnect-ctxhyp
    Write-Warning "Exiting script"
    exit 1
}

# Get Storage Repository to migrate VM to (usually the same if in the same pool)
$sr2ref = get-hypSR -xenSRName $XenServer_SRName | ConvertTo-XenRef
if ($null -eq $sr2ref) {
    Write-Warning "XenServer Storage Repository [$XenServer_SRName] was not correct. Try another SR name."
    disconnect-ctxhyp
    Write-Warning "Exiting script"
    exit 1
}

#region main
$hostsToBalance = get-ctxHypVMTable -hypSession $session
$totalHosts = $hostsToBalance.count
$vms = Get-XenVM | Where-Object { $_.is_a_snapshot -eq $false -and $_.is_a_template -eq $false -and $_.is_control_domain -eq $false }
$vdas = $vms | Where-Object { $_.is_a_snapshot -eq $false -and $_.is_a_template -eq $false -and $_.is_control_domain -eq $false } | Select-Object name_label | Sort-Object name_label
$totalVms = $vdas.count
$optimalVMCount = [math]::Round($totalVms / $totalHosts)

Write-Host "Optimizing XS Pool: [$xsn]"
Write-Host "Number of hosts: [$totalHosts]"
Write-Host "Number of virtual machines: [$totalVms]"
Write-Host "Optimal VMs to Host count: [$optimalVMCount]"

# Get set of hypervisors with fewer and more than $optimalVMCount
$DestinationHypervisors = get-ctxHypDest -idealNumberOfVMs $optimalVMCount -hypTable $hostsToBalance
$SourceHypervisors = get-ctxHypSource -idealNumberOfVMs $optimalVMCount -hypTable $hostsToBalance

# Balance VMs
foreach ($srchyp in $SourceHypervisors) {
    while ($srchyp.VMCount -gt $optimalVMCount) {
        foreach ($desthyp in $DestinationHypervisors) {
            if ($desthyp.VMCount -lt $optimalVMCount) {
                $srcVM = get-vmToMigrate -hypTableRow $srchyp -vmSR $sr2ref
                [string]$tmpName = $srcvm.vmToMigrate.name_label
                $destHypHost = get-destHyp -hypTableRow $desthyp -hypNet $xennet
                Write-Verbose "Migrating [$tmpName]"
                $migrateTask = invoke-vmMigration -VMtoMigrate $srcVM.vmToMigrate -DestinationHost $destHypHost -VMVIFMap $vifmap -VMVDIMap $srcVM.vdiMap -hpySession $session
                Wait-XenTask -Task $migrateTask -ShowProgress
                $desthyp.VMCount++
                $srchyp.VMCount--
                Write-Verbose "---------------------------------------"
                Write-Verbose "Source Host"
                $srchyp | Select-Object -Property *
                Write-Verbose "Destination Host"
                $desthyp | Select-Object -Property *
                Write-Verbose "---------------------------------------"
                break
            }
        }
    }
}

#endregion

#Disconnect from XenServer
disconnect-ctxhyp

#End script info
Write-Verbose "SCRIPT NAME: $scriptName"
Write-Verbose "SCRIPT PATH: $scriptPath"
Write-Verbose "SCRIPT RUNTIME: $datetime"
Write-Verbose "SCRIPT USER: $ScriptRunner"
Write-Verbose "SCRIPT SYSTEM: $compname.$domain"