DSC_Disk trigers defrag

[Fiander]

Problem description

we use the storage dsc to configure disks.
but each time it runs (Test-targetResource), it triggers a defrag. This can be seen in the eventlog.

i have traced it down to the Get-PartitionSupportedSize cmdlet. The doc at MS conform this. "This cmdlet starts the "Optimize Drive" (defragsvc) service. This could lead to longer execution time on larger fragmented drives."

This defrag makes the dsc module slow and uses a lot of disk IO.

I'm sorry, but our environment is an offline one, i cannot post much info about it.

edit: just seen it is a known problem, the fix will stil work.

Verbose logs

this is not in the log. you can see it in the application eventlog.

Get-PartitionSupportedSize  -DiskNumber 0 -PartitionNumber 4 triggers it for me, but any disk/partition with a (ntfs) volume on it will do.

DSC configuration

Disk JVolume
        {
             DiskId = 2
             DriveLetter = 'J'
             FSLabel = 'Data'
        }

Suggested solution

Replace
Get-PartitionSupportedSize

with
$(get-partition).size
in the disk resource.

on my system the results are:
[math]::Truncate( $( Get-PartitionSupportedSize -DiskNumber 0 -PartitionNumber 4).SizeMax /1MB )
129432

[math]::Truncate($(get-partition -DiskNumber 0 -PartitionNumber 4).size /1MB)
129432

When changed to MB, there is no difference between the two.

when measured :
Measure-Command {
[math]::Truncate( $( Get-PartitionSupportedSize -DiskNumber 0 -PartitionNumber 4).SizeMax /1024/1024 )# for MB
}
Days : 0
Hours : 0
Minutes : 0
Seconds : 40
Milliseconds : 54
Ticks : 400545516
TotalDays : 0.000463594347222222
TotalHours : 0.0111262643333333
TotalMinutes : 0.66757586
TotalSeconds : 40.0545516
TotalMilliseconds : 40054.5516

Measure-Command {
[math]::Truncate($(get-partition -DiskNumber 0 -PartitionNumber 4).size /1024/1024)
}
Days : 0
Hours : 0
Minutes : 0
Seconds : 0
Milliseconds : 167
Ticks : 1677114
TotalDays : 1.94110416666667E-06
TotalHours : 4.65865E-05
TotalMinutes : 0.00279519
TotalSeconds : 0.1677114
TotalMilliseconds : 167.7114

From 40+ seeconds to almost instant.

The added "/1MB" and Truncate should also "fix" the size difference mentioned in #181

But this would not allow the disk to be extended.
row 812 is now:
$supportedSize = ($partition | Get-PartitionSupportedSize)
this could be:

$diskSize = [math]::Truncate($disk.size /1GB)
$totalSize = [math]::Truncate($(Get-Partition -DiskId $DiskId | measure-object -sum -Property size).Sum /1GB)

if($diskSize -gt $totalSize)
{
    $supportedSize = ($partition | Get-PartitionSupportedSize)
}
else
{
        $supportedSize = [pscustomobject]@{
        SizeMin = $partition.Size
        SizeMax = $partition.Size
    }
}

This would only run the Get-PartitionSupportedSize when there is free room on the disk.
When all space on the disk is used for partitions, there is no need to run the expensive get-partitionSupportedSize

Operating system the target node is running

tried this on windows 10, 2012 2016 2019

From https://docs.microsoft.com/en-us/powershell/module/storage/get-partitionsupportedsize?view=winserver2012-ps :
This cmdlet starts the "Optimize Drive" (defragsvc) service. This could lead to longer execution time on larger fragmented drives.

From https://docs.microsoft.com/en-us/powershell/module/storage/get-partitionsupportedsize?view=windowsserver2022-ps :
This cmdlet starts the "Optimize Drive" (defragsvc) service. This could lead to longer execution time on larger fragmented drives.

This is as designed. dont know why. but it is what it is........

PowerShell version and build the target node is running

5.1 6 and 7 all the same.

StorageDsc version

most recent. ( 5.01 )

[PlagueHO]

Hi @Fiander - thank you for raising this. That is really useful information.

I'm thinking we could put this into a new support function Get-PartitionSupportedSizeAvoidDefrag (although I'm not a fan of the name). This would allow easier unit testing.

Happy to take a PR for this.