{"id":30,"date":"2025-08-17T02:27:19","date_gmt":"2025-08-17T02:27:19","guid":{"rendered":"http:\/\/vinpearl.ca\/?p=30"},"modified":"2025-08-17T18:59:30","modified_gmt":"2025-08-17T18:59:30","slug":"problem-ejecting-usb-attached-scsi-uas-mass-storage-device","status":"publish","type":"post","link":"https:\/\/vinpearl.ca\/index.php\/2025\/08\/17\/problem-ejecting-usb-attached-scsi-uas-mass-storage-device\/","title":{"rendered":"Problem Ejecting USB Attached SCSI (UAS) Mass Storage Device"},"content":{"rendered":"\n
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Warning 8\/16\/2025 7:24:04 PM Kernel-PnP 225 (223)<\/p>\n\n\n\n

Log Name: System
Source: Microsoft-Windows-Kernel-PnP
Date: 8\/16\/2025 7:24:04 PM
Event ID: 225
Task Category: (223)
Level: Warning
Keywords:
User: SYSTEM
Computer: jujube
Description:
The application \\Device\\HarddiskVolume3\\Windows\\System32\\dllhost.exe with process id 9176 stopped the removal or ejection for the device USB\\VID_174C&PID_55AA\\MSFT30123458DB27C1.
Process command line: C:\\Windows\\system32\\DllHost.exe \/Processid:{DFB65C4C-B34F-435D-AFE9-A86218684AA8}
List of affected devices:<\/p>\n\n\n\n

Event Xml:
225 2 3 223 0 0x8000000000000000 699231 System jujube 9176 52 \\Device\\HarddiskVolume3\\Windows\\System32\\dllhost.exe 40 USB\\VID_174C&PID_55AA\\MSFT30123458DB27C1 81 C:\\Windows\\system32\\DllHost.exe \/Processid:{DFB65C4C-B34F-435D-AFE9-A86218684AA8} 0<\/p>\n\n\n\n

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dllhost.exe<\/code>?
It\u2019s the COM Surrogate<\/strong> process in Windows.
Runs COM objects outside the main process for stability (if the COM object crashes, it won\u2019t take down Explorer).
Commonly used by Explorer<\/strong> to generate thumbnails, previews, and metadata<\/strong> (especially for videos, images, Office docs, PDFs, etc.).
So if your USB contains pictures, videos, or documents, Explorer may spawn dllhost.exe<\/code> to read the files<\/strong> \u2192 and this keeps the drive \u201cbusy,\u201d blocking ejection.

Preventive Fixes
Disable thumbnail previews<\/strong> (since dllhost<\/code> is often generating them):<\/figcaption><\/figure>\n\n\n\n

Why dllhost.exe<\/code> Stays Alive After Explorer is Closed<\/mark><\/p>\n\n\n\n

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CLSID & AppID<\/mark>:CLSID (Class ID)<\/strong> \u2192 points to a COM class (e.g., thumbnail handler, metadata handler). Under it you usually see InProcServer32<\/code> \u2192 the DLL actually being loaded.
AppID (Application ID)<\/strong> \u2192 groups one or more CLSIDs under a logical \u201capplication\u201d for COM security and activation. It doesn\u2019t always have a friendly name.<\/figcaption><\/figure>\n\n\n\n

HKEY_CLASSES_ROOT\\CLSID
HKEY_LOCAL_MACHINE\\SOFTWARE\\Classes\\CLSID
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“Plan9FileSystem” in Windows?<\/mark><\/h2>\n\n\n\n