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function Test-DbaDiskAlignment {
Verifies that your non-dynamic disks are aligned according to physical constraints.
Returns $true or $false by default for one server. Returns Server name and IsBestPractice for more than one server.
Please refer to your storage vendor best practices before following any advice below.
By default issues with disk alignment should be resolved by a new installation of Windows Server 2008, Windows Vista, or later operating systems, but verifying disk alignment continues to be recommended as a best practice.
While some versions of Windows use different starting alignments, if you are starting anew 1MB is generally the best practice offset for current operating systems (because it ensures that the partition offset % common stripe unit sizes == 0 )
* Dynamic drives (or those provisioned via third party software) may or may not have accurate results when polled by any of the built in tools, see your vendor for details.
* Windows does not have a reliable way to determine stripe unit Sizes. These values are obtained from vendor disk management software or from your SAN administrator.
* System drives in versions previous to Windows Server 2008 cannot be aligned, but it is generally not recommended to place SQL Server databases on system drives.
.PARAMETER ComputerName
The target computer or computers.
.PARAMETER Credential
Specifies an alternate Windows account to use when enumerating drives on the server. May require Administrator privileges. To use:
$cred = Get-Credential, then pass $cred object to the -Credential parameter.
Login to the target instance using alternative credentials. Windows and SQL Authentication supported. Accepts credential objects (Get-Credential)
If this switch is enabled, the disk(s) will not be checked for SQL Server data or log files.
.PARAMETER EnableException
By default, when something goes wrong we try to catch it, interpret it and give you a friendly warning message.
This avoids overwhelming you with "sea of red" exceptions, but is inconvenient because it basically disables advanced scripting.
Using this switch turns this "nice by default" feature off and enables you to catch exceptions with your own try/catch.
Tags: Storage
Author: Constantine Kokkinos (@mobileck),
Copyright: (c) 2018 by dbatools, licensed under MIT
License: MIT
The preferred way to determine if your disks are aligned (or not) is to calculate:
1. Partition offset - stripe unit size
2. Stripe unit size - File allocation unit size
- Disk Partition Alignment Best Practices for SQL Server -
- Getting Partition Offset information with Powershell -
Thanks to Jonathan Kehayias!
- Decree: Set your partition Offset and block Size and make SQL Server faster -
Thanks to Jen McCown!
- Disk Performance Hands On -
Thanks to Kendal Van Dyke!
- Get WMI Disk Information -
Thanks to jbruns2010!
PS C:\> Test-DbaDiskAlignment -ComputerName sqlserver2014a
Tests the disk alignment of a single server named sqlserver2014a
PS C:\> Test-DbaDiskAlignment -ComputerName sqlserver2014a, sqlserver2014b, sqlserver2014c
Tests the disk alignment of multiple servers
param (
[parameter(Mandatory, ValueFromPipeline)]
[Alias("ServerInstance", "SqlServer", "SqlInstance")]
begin {
Test-DbaDeprecation -DeprecatedOn "1.0.0" -Parameter 'Detailed'
$sessionoption = New-CimSessionOption -Protocol DCom
function Get-DiskAlignment {
param (
[string]$FunctionName = (Get-PSCallStack)[0].Command,
[bool]$EnableException = $EnableException
$SqlInstances = @()
$offsets = @()
#region Retrieving partition/disk Information
try {
Write-Message -Level Verbose -Message "Gathering information about first partition on each disk for $ComputerName." -FunctionName $FunctionName
try {
$partitions = Get-CimInstance -CimSession $CimSession -ClassName Win32_DiskPartition -Namespace "root\cimv2" -ErrorAction Stop
} catch {
if ($_.Exception -match "namespace") {
Stop-Function -Message "Can't get disk alignment info for $ComputerName. Unsupported operating system." -InnerErrorRecord $_ -Target $ComputerName -FunctionName $FunctionName
} else {
Stop-Function -Message "Can't get disk alignment info for $ComputerName. Check logs for more details." -InnerErrorRecord $_ -Target $ComputerName -FunctionName $FunctionName
$disks = @()
$disks += $($partitions | ForEach-Object {
Get-CimInstance -CimSession $CimSession -Query "ASSOCIATORS OF {Win32_DiskPartition.DeviceID=""$($_.DeviceID.Replace("\", "\\"))""} WHERE AssocClass = Win32_LogicalDiskToPartition" |
Add-Member -Force -MemberType noteproperty -Name BlockSize -Value $_.BlockSize -PassThru |
Add-Member -Force -MemberType noteproperty -Name BootPartition -Value $_.BootPartition -PassThru |
Add-Member -Force -MemberType noteproperty -Name DiskIndex -Value $_.DiskIndex -PassThru |
Add-Member -Force -MemberType noteproperty -Name Index -Value $_.Index -PassThru |
Add-Member -Force -MemberType noteproperty -Name NumberOfBlocks -Value $_.NumberOfBlocks -PassThru |
Add-Member -Force -MemberType noteproperty -Name StartingOffset -Value $_.StartingOffset -PassThru |
Add-Member -Force -MemberType noteproperty -Name Type -Value $_.Type -PassThru
} |
Select-Object BlockSize, BootPartition, Description, DiskIndex, Index, Name, NumberOfBlocks, Size, StartingOffset, Type
Write-Message -Level Verbose -Message "Gathered CIM information." -FunctionName $FunctionName
} catch {
Stop-Function -Message "Can't connect to CIM on $ComputerName." -FunctionName $FunctionName -InnerErrorRecord $_
#endregion Retrieving partition Information
#region Retrieving Instances
if (-not $NoSqlCheck) {
Write-Message -Level Verbose -Message "Checking for SQL Services." -FunctionName $FunctionName
$sqlservices = Get-CimInstance -ClassName Win32_Service -CimSession $CimSession | Where-Object DisplayName -like 'SQL Server (*'
foreach ($service in $sqlservices) {
$instance = $service.DisplayName.Replace('SQL Server (', '')
$instance = $instance.TrimEnd(')')
$instancename = $instance.Replace("MSSQLSERVER", "Default")
Write-Message -Level Verbose -Message "Found instance $instancename" -FunctionName $FunctionName
if ($instance -eq 'MSSQLSERVER') {
$SqlInstances += $ComputerName
} else {
$SqlInstances += "$ComputerName\$instance"
$sqlcount = $SqlInstances.Count
Write-Message -Level Verbose -Message "$sqlcount instance(s) found." -FunctionName $FunctionName
#endregion Retrieving Instances
#region Offsets
foreach ($disk in $disks) {
if (!$"\\")) {
$diskname = $disk.Name
if ($NoSqlCheck -eq $false) {
$sqldisk = $false
foreach ($SqlInstance in $SqlInstances) {
try {
if ($null -ne $SqlCredential) {
$smoserver = Connect-SqlInstance -SqlInstance $SqlInstance -SqlCredential $SqlCredential
} else {
$smoserver = Connect-SqlInstance -SqlInstance $SqlInstance # win auth
$sql = "Select count(*) as Count from sys.master_files where physical_name like '$diskname%'"
Write-Message -Level Verbose -Message "Query is: $sql" -FunctionName $FunctionName
Write-Message -Level Verbose -Message "SQL Server is: $SqlInstance." -FunctionName $FunctionName
$sqlcount = $smoserver.Databases['master'].ExecuteWithResults($sql).Tables[0].Count
if ($sqlcount -gt 0) {
$sqldisk = $true
} catch {
Stop-Function -Message "Can't connect to $ComputerName ($SqlInstance)." -FunctionName $FunctionName -InnerErrorRecord $_
if ($NoSqlCheck -eq $false) {
if ($sqldisk -eq $true) {
$offsets += $disk
} else {
$offsets += $disk
#endregion Offsets
#region Processing results
Write-Message -Level Verbose -Message "Checking $($offsets.count) partitions." -FunctionName $FunctionName
foreach ($partition in $offsets) {
# Unfortunately "Windows does not have a reliable way to determine stripe unit Sizes. These values are obtained from vendor disk management software or from your SAN administrator."
# And this is the #1 most impactful issue with disk alignment :D
# What we can do is test common stripe unit Sizes against the Offset we have and give advice if the Offset they chose would work in those scenarios
$offset = $partition.StartingOffset / 1kb
$type = $partition.Type
$stripe_units = @(64, 128, 256, 512, 1024) # still wish I had a better way to verify this or someone to pat my back and say its alright.
# testing dynamic disks, everyone states that info from dynamic disks is not to be trusted, so throw a warning.
Write-Message -Level Verbose -Message "Testing for dynamic disks." -FunctionName $FunctionName
if ($type -eq "Logical Disk Manager") {
$IsDynamicDisk = $true
Write-Message -Level Warning -Message "Disk is dynamic, all Offset calculations should be suspect, please refer to your vendor to determine actual Offset calculations." -FunctionName $FunctionName
} else {
$IsDynamicDisk = $false
Write-Message -Level Verbose -Message "Checking for best practices offsets." -FunctionName $FunctionName
if ($offset -ne 64 -and $offset -ne 128 -and $offset -ne 256 -and $offset -ne 512 -and $offset -ne 1024) {
$IsOffsetBestPractice = $false
} else {
$IsOffsetBestPractice = $true
# as we can't tell the actual size of the file strip unit, just check all the sizes I know about
foreach ($size in $stripe_units) {
if ($offset % $size -eq 0) {
# for proper alignment we really only need to know that your offset divided by your stripe unit size has a remainder of 0
$OffsetModuloKB = "$($offset % $size)"
$isBestPractice = $true
} else {
$OffsetModuloKB = "$($offset % $size)"
$isBestPractice = $false
ComputerName = $ogcomputer
Name = "$($partition.Name)"
PartitonSize = [dbasize]($($partition.Size / 1MB) * 1024 * 1024)
PartitionType = $partition.Type
TestingStripeSize = [dbasize]($size * 1024)
OffsetModuluCalculation = [dbasize]($OffsetModuloKB * 1024)
StartingOffset = [dbasize]($offset * 1024)
IsOffsetBestPractice = $IsOffsetBestPractice
IsBestPractice = $isBestPractice
NumberOfBlocks = $partition.NumberOfBlocks
BootPartition = $partition.BootPartition
PartitionBlockSize = $partition.BlockSize
IsDynamicDisk = $IsDynamicDisk
process {
# uses cim commands
foreach ($computer in $ComputerName) {
$computer = $ogcomputer = $computer.ComputerName
Write-Message -Level VeryVerbose -Message "Processing: $computer."
$computer = Resolve-DbaNetworkName -ComputerName $computer -Credential $Credential
$Computer = $computer.FullComputerName
if (-not $Computer) {
Stop-Function -Message "Couldn't resolve hostname. Skipping." -Continue
#region Connecting to server via Cim
Write-Message -Level Verbose -Message "Creating CimSession on $computer over WSMan"
if (-not $Credential) {
$cimsession = New-CimSession -ComputerName $Computer -ErrorAction Ignore
} else {
$cimsession = New-CimSession -ComputerName $Computer -ErrorAction Ignore -Credential $Credential
if ($null -eq $ {
Write-Message -Level Verbose -Message "Creating CimSession on $computer over WSMan failed. Creating CimSession on $computer over DCOM."
if (!$Credential) {
$cimsession = New-CimSession -ComputerName $Computer -SessionOption $sessionoption -ErrorAction Ignore
} else {
$cimsession = New-CimSession -ComputerName $Computer -SessionOption $sessionoption -ErrorAction Ignore -Credential $Credential
if ($null -eq $ {
Stop-Function -Message "Can't create CimSession on $computer." -Target $Computer -Continue
#endregion Connecting to server via Cim
Write-Message -Level Verbose -Message "Getting Power Plan information from $Computer."
try {
Get-DiskAlignment -CimSession $cimsession -NoSqlCheck $NoSqlCheck -ComputerName $Computer -ErrorAction Stop
} catch {
Stop-Function -Message "Failed to process $($Computer): $($_.Exception.Message)" -Continue -InnerErrorRecord $_ -Target $Computer
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