IUpdate::get_MaxDownloadSize returning 100s of GBs

Question

IUpdate::get_MaxDownloadSize returning 100s of GBs

Tea 1

When utilizing https://learn.microsoft.com/en-us/windows/win32/api/wuapi/nf-wuapi-iupdate-get_maxdownloadsize, some updates are retuning 100s of GBs despite the Microsoft Update Catalog not showing such sizes.

For example:
ID: "8da25b5f-b5e1-455e-9ae9-7697212593d7"
PATCH: "2022-08 Cumulative Update for Windows 11 for x64-based Systems (KB5016629)"
MAX: "130944369686"

https://www.catalog.update.microsoft.com/Search.aspx?q=KB5016629 shows:
Size of no greater than 405.2 MB.

Why does the API return such a large value?
Is this expected behavior?

No errors are being returned when this API is called.

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3 answers

Your answer

Answer 1

abbodi86 5,101

Unified Update Platform

starting with Windows 10 v1709, each Cumulative Update bundle include the full set of UUP files which represent complete OS installation files, for all languages, all Features on Demand, plus the regular updates files (in all fomats together, express/full/baseless)

the returned size is pretty much correct

of course, actual Windows Update installation would only download the required "updates" files (which used express update mechanism up to Win10 v1803, before switching to PSFX format with Win10 v1809)

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Answer 2

Jeanine Zhang-MSFT 11,356 Microsoft External Staff

@Tea

The MaxDownloadSize property is not always downloaded. The MaxDownloadSize property is downloaded based on the configuration of the computer that receives the update. As far as I'm concerned, it is normal phenomenon.

I suggest you could refer to the thread: https://social.technet.microsoft.com/Forums/windows/en-US/1330f75f-7899-457e-a772-8cfc673a7cf1/windows-update-agent-returns-wrong-size-of-updates

Tea 1 Reputation point

2022-09-26T18:59:41.38+00:00

The Microsoft catalog update contains the full update from my understanding.

112 GB for a cumulative update is extreme and does not appear to be the correct size for what is downloaded to my system, but I seem to lack to ability to calculate the maximum download size from the winAPIs. I understand the MaxDownloadSize property is downloaded based on the configuration of the computer that receives the update but I am at a lost for how this is actually calculated since it appears to be incorrect.
Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2022-09-28T08:56:38.39+00:00

@Tea

As far as I'm concerned, the MaxDownloadSize aontains all updated information (applicable and inapplicable). And the WUA API search returns the update information (Title) applicable to the computer.
Tea 1 Reputation point

2022-10-03T18:04:12.507+00:00

@Jeanine Zhang-MSFT Is there away I can calculate the expected download size of a patch per my system?
Chris Williams 0 Reputation points

2023-03-03T20:03:10.61+00:00

The example Tea gave above shows a MaxFileSize of 130944369686 bytes, or 130.94 GB(!). I could download the entire Win11 OS image multiple times before getting to 131 GB.

The Update Catalog shows a file size of 405 MB for the same update.

I'm having the same issue with multiple updates. For example, KB5022840 on Server 2019 shows a MaxFileSize of 16.45 GB. The ISO image for Server 2019 is 5.3 GB. The Update Catalog shows 596 MB instead.

This looks like a bug in behavior.

Answer 3

Michael Taylor 61,236

This is because of how Windows updates work (and have for a while now). A full discussion is beyond this post but you can get the highlights from here.

The gist of it is that in a perfect world you are running current OS versions with updates. Therefore the get_MinDownloadSize returns the minimum size needed to apply the update. However the update has to account for all the variants including you missing updates. Therefore it may have to download more than the minimal. In the worst case it'll down get_MaxDownloadSize of data which is the entire update. But this shouldn't be common.

If you're trying to figure out how much space to reserve for the update then consider using get_RecommendedHardDiskSpace instead.

Tea 1 Reputation point

2022-09-20T14:10:53.18+00:00

@Michael Taylor get_MinDownloadSize and get_RecommendedHardDiskSpace return 0 in this scenario.
Michael Taylor 61,236 Reputation points

2022-09-20T14:15:37.487+00:00

That's possible. The update you call it on may not apply and hence the size is 0. If you can provide your code and the example update that you're having an issue with then perhaps we can help more.
Tea 1 Reputation point

2022-09-21T14:47:17.267+00:00
@Michael Taylor
This can be seen with just a simple powershell script:

$Searcher = New-Object -ComObject Microsoft.Update.Searcher $Results = $Searcher.Search("IsInstalled=0") Foreach ($update in $Results.Updates) { Write-Host "Title :" $update.Title Write-Host "Min: " $update.MinDownloadSize Write-Host "Max: " $update.MaxDownloadSize Write-Host "DiskSpace: " $update.RecommendedHardDiskSpace }

For example:
Title : 2022-08 Cumulative Update for Windows 10 Version 20H2 for x64-based Systems (KB5016616)
Min: 0
Max: 112349313302
DiskSpace: 0

Max for this cumulative update shows as 112 GB.
https://www.catalog.update.microsoft.com/Search.aspx?q=KB5016616
But the catalog never goes above 738MB.
Michael Taylor 61,236 Reputation points

2022-09-23T13:57:22.437+00:00

I'm not sure where the sizes come from on the site you linked to but they aren't correct based upon a couple of tests. I downloaded a few and the actual downloaded files more closely match what the update service is returning as max size. Since the update site doesn't scan your machine it would need to download the "full" update. Hence I would expect it to be closer to the max download size.
Tea 1 Reputation point

2022-09-26T18:59:14.667+00:00

The Microsoft catalog update contains the full update from my understanding.

112 GB for a cumulative update is extreme and does not appear to be the correct size for what is downloaded to my system, but I seem to lack to ability to calculate the maximum download size from the winAPIs. I understand the MaxDownloadSize property is downloaded based on the configuration of the computer that receives the update but I am at a lost for how this is actually calculated since it appears to be incorrect.