在Azure VM上使用Powershell不稳定文件下载

Question

I'm noticing some strange behavior on an Azure Virtual Machine when downloading a file using the Invoke-WebRequest command. Seems like the download stream is super choppy. Normally, Azure VMs download files super fast, so not sure what's causing this. The file lives in azure blob storage in the same region as the VM. When I download the file via web browser, it only takes 3 seconds. Using powershell takes about a minute!

Here is a screen capture of the network when done using powershell.

To clarify, this is the code I'm using to download a file...

$dest = "$($buildDir)\MyStuff.zip"
Invoke-WebRequest "https://mystorage.blob.core.windows.net/apps/$($using:buildNumber)/App/MyStuff.zip" -OutFile $dest

I'm using whatever version of powershell comes on the 2016-Datacenter image in the azure gallery.

Answer 1

Yes, PowerShell cmdlet Invoke-WebRequest download files slow than web browser, because the progress reporting every byte, the overhead is high than others(web browser).

More information about speed of Invoke-WebRequest , please refer to the answer of @jasongin .

If you want to download file via PowerShell, maybe we can use WebClient Class , that will fast than WebRequest Class , we can use command like this:

$download = New-Object net.webclient  
$download.Downloadfile($source_url, $local_url)

Hope this helps.

Answer 2

You do not show your code on how you are using Invoke-WebRequest or if you are using 32 vs 64bit.

From a similar post with an accepted answer of...

"The issue is that he's piping COM objects into another cmdlet – in this case, Select-Object. When that happens, we attempt to bind parameters by property name. Enumerating property names of a COM object is brutally slow – so we're spending 86% of our time on two very basic CLR API calls:

(…) // Get the function description from a COM type typeinfo.GetFuncDesc(index, out pFuncDesc); (…) // Get the function name from a COM function description typeinfo.GetDocumentation(funcdesc.memid, out strName, out strDoc, out id, out strHelp); (…)

We might be able to do something smart here with caching.

A workaround is to not pipe into Select-Object, but instead use language features: Grab the rows from the table, skipping the first row (column headers)

$allRows = @($slotTable.getElementsByTagName("tr"))
$rows = $allRows[1..$allRows.Count]

Why is this PowerShell code (Invoke-WebRequest / getElementsByTagName) so incredibly slow on my machines, but not others?

But in general Invoke-WebRequest in 5.1 and below is slow. In PoSHv6(Core) it is way faster. Try is for yourself and see.

There are several articles on line the specifically talk to how slow Invoke-WebRequest can be.

Invoke-WebRequest speed seems slow compare to Windows version but is not https://github.com/PowerShell/PowerShell/issues/5284 https://github.com/PowerShell/PowerShell/issues/2656 https://www.chasewright.com/invoke-webrequest-vs-system-net-webclient-download-speed