Measuring LUNS

[Guv]

I am trying to measure performance of our datastores and luns of our esx hosts. I am using the function below for measuring diskreadlatency and diskwritelatency :

function Get-VMHostLunLatency {

param($VMHost)

$luns = $VMHost | Get-ScsiLun

foreach ($lun in $luns) {

$stats = $VMHost |

Get-Stat -stat disk.totalreadlatency.average,disk.totalwritelatency.average -maxsamples 1 -realtime |

Where { $_.Instance -eq $Lun.CanonicalName }

if ($stats.length -ne $null) {

$obj = New-Object PSObject

$obj | Add-Member -MemberType NoteProperty -Name Lun -Value $lun.CanonicalName

$obj | Add-Member -MemberType NoteProperty -Name ReadLatency -Value ($stats[0].Value)

$obj | Add-Member -MemberType NoteProperty -Name WriteLatency -Value ($stats[1].Value)

Write-Output $obj

}

}

}

Then use:

Get-VMHostLunLatency -vmhost (get-vmhost "esxhost" ) | Format-Table -Autosize *

When I run the above it lists all the LUNS for the esx hosts, but the values for readlatency and writelatency are all mainly 0, there are few values such as 4 or 5. Does this mean there is no latency for my luns at the moment, or is there any issue with measuring latency. Just want to make sure.

Thanks

[LucD]

Can't you cross-check with the vSphere client or with esxtop ?

____________

Blog: LucD notes

Twitter: lucd22

[Guv]

Yes I will check on vpshere client

[LucD]

Had a closer look at your script and made a few changes.

function Get-VMHostLunLatency {
	param($VMHost)

	$luns = $VMHost | Get-ScsiLun
	$statsAll = Get-Stat -Entity $VMHost -stat disk.totalreadlatency.average,disk.totalwritelatency.average -maxsamples 1 -realtime
	foreach ($lun in $luns) {
		$statsLun = $statsAll | where { $_.Instance -eq $Lun.CanonicalName }
		if ($statsLun.length -ne $null) {
			$obj = New-Object PSObject
			$obj | Add-Member -MemberType NoteProperty -Name Lun -Value $lun.CanonicalName
			$obj | Add-Member -MemberType NoteProperty -Name ReadLatency -Value ($statsLun | where{$_.MetricId -eq "disk.totalreadlatency.average"}).Value
			$obj | Add-Member -MemberType NoteProperty -Name WriteLatency -Value ($statsLun | where{$_.MetricId -eq "disk.totalwritelatency.average"}).Value
			$obj
		}
	}
}

Get-VMHostLunLatency -vmhost (get-vmhost <esx-hostname> ) | Format-Table -Autosize

You only have to call Get-Stat once which will make the script faster.

For each Lun it extracts the statistics for that specific Lun in the $statsLun variable.

You can be sure that readlatency will always be the first value in the array. This way you're always sure.

Btw, I also see mos of the time zero values.

Which is good, there is nearly no latency on the Luns.

____________

Blog: LucD notes

Twitter: lucd22