
OneDrive for Business is different from personal Ondrive, it is a personal SharePoint site collection, so if you log into it online, the URL would include "my.sharepoint.com", like following image.
is that mean my files are saved in sharepoint instead of onedrive?
For OneDrive for Business , I think your are right.
whether the admin can view/access the files i've uploaded here?
As OneDrive for Business is managed by your organization, the site collection administrators can control what you can do in the library.
Under certain circumstances, the administrators can access your OneDrive data. For more detailed information, you may refer to "Step 4 - Give another employee access to OneDrive and Outlook data".
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