Oho! Sometimes, it’s nice to be proved correct, even if it takes a while. Last October, I posted at Win10.Guru about a “PortableBaseLayer” partition. At that time, I reported that “one theory about this partition is tied to Reserved Storage for Windows Update.” On February 26, an MS DOCS item appeared that illuminates the whole subject. It’s entitled DISM Reserved Storage Command-line Options. Here’s a screencap of what PowerShell looks like once this capability is enabled in Windows 10 2004 (Release Preview, Build 19582):
The /Get-ReservedStorageState cmdlet tells you if such space has been reserved (state: enabled) or not (state: disabled).
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Understanding DISM ReservedStorage Commands
In PowerShell, where there’s a Get- cmdlet, there’s also usually a Set- cmdlet as well. That’s certainly true of ReservedStorage cmdlets. But before we venture into syntax details in the next section, here’s what the DOCS file has to say about the history and capabilities of ReservedStorage itself:
With the release of Windows 10, version 1903, Microsoft introduced reserve storage for newly manufactured PCs, and Windows 10 clean installations. Reserved storage increases the likelihood that Windows 10 updates can be downloaded and installed without users having to free disk space.
With the Windows 10, version 2004 release, a new set of DISM commands are available, to enable IT pros to enable and disable reserved storage on demand. This includes devices that were not shipped with Windows 10, version 1903 and higher. For devices that connect directly to Windows Update (WU), reserved storage works out of the box. However, for IT managed devices, using endpoint management tools such as Windows Server Update Services or ConfigMgr, reserved storage does not work automatically. For these environments, endpoint management tools can leverage reserved storage by disabling it prior to downloading and installing an update, followed by enabling reserved storage when the update installation has completed.
An MS Support note entitled How reserved storage works in Windows 10 (dated May 2019, interestingly enough) explains further:
To make sure your device can successfully update and that it runs its best, Windows reserves a portion of storage space on your device for use by temporary files, caches, and other files. When your device is low on space, Windows will clear reserved storage so it can be used for other processes, like a Windows update. Reserving storage also helps keep disk space usage on your device more predictable and more stable.
The ultimate reference on this topic appears in an April 2019 MS Tech Community note entitled Windows 10 and reserved storage. I’ll forgo reproducing that, and leave it for the real die-hards to read.
Where Does ReservedStorage Reside?
Though there’s no separate partition for this space in the disk layout any more, it’s safe to guess that the space gets allocated on the C: drive. I wouldn’t be surprised if it was 8 GB in size (the same size as that now-defunct PortableBaseLayer partition, in other words). So I went looking in the System Volume Information folder as the most likely place to find the reservation. I believe it shows up as a series of GUID named files therein, as shown in TreeSize. Because I enabled ReservedStorage on Monday, March 9, I it’s possible that the 2.1 GB file with that creation date is could hold that reservation right now. Honestly, I just don’t know for sure. I’ll keep digging and see what I can learn.
My best guess is that a reservation would most likely reside in System Volume Information, a folder Windows 10 uses for all kinds of hidden system functions.
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[Note added March 13 3:00 PM] Found more info, thanks to Martin Brinkmann at Ghacks.net. If you enable Reserved Storage, then click Settings → System → Storage → Show more categories → Click on System & reserved you’ll see information on Reserved Storage. Note further that the learn about link goes to the MS Support note I cited earlier in this story. Inside of Settings, information about Reserved Storage looks like this:
This info panel from Settings clearly shows reserved storage at 7.25 GB. If I add
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I don’t understand how (or even if) this maps into the files in the System Volume Information folder. I’m guessing Windows 10 is holding that reservation somewhere else. Sooner or later, I will find where it lives.
Digging into Details for DISM ReservedStorage Commands
There are two DISM options related to ReservedStorageState. First, /Set-ReservedStorageState may either be enabled or disabled, using the /State parameter. Here’s how the DOCS file shows this command at work (it’s self-explanatory):
DISM.exe /Online /Set-ReservedStorageState /State:Enabled
DISM.exe /Online /Set-ReservedStorageState /State:Disabled
The /Get-ReservedStorageState is purely a reporting function, so it takes no options or arguments. It simply reports whether or not the ReservedStorageState is — you guessed it — enabled or disabled. As DISM options go these are about as simply as things get. You can use them in 2004 Insider Preview releases right now, but they won’t become generally available until 2004 goes into General Availability later this Spring. Stay tuned!
Author: Ed Tittel
Ed Tittel is a 30-plus-year computer industry veteran. He’s a Princeton and multiple University of Texas graduate who’s worked in IT since 1981 when he started his first programming job. Over the past three decades he’s also worked as a manager, technical evangelist, consultant, trainer, and an expert witness. See his professional bio for all the details.