It sounds like you're experiencing significant issues with BitLocker on your HDDs after installing Windows 11. BitLocker is designed to provide encryption and security for drives, but it can sometimes lead to performance issues, especially on certain hardware configurations.
In Windows 11, BitLocker can automatically encrypt internal drives after the Out Of Box Experience (OOBE), but it requires users to sign in with a Microsoft Account or an Azure Active Directory account for the protection to be enabled. If you are using local accounts, BitLocker may not automatically enable, and you can manually manage it through the BitLocker Control Panel.
If you are facing performance issues with HDDs, it may be beneficial to disable BitLocker or avoid using it on those drives. Additionally, for troubleshooting, you might want to check if there are any group policy settings or registry settings that could be affecting BitLocker’s behavior on your system.
It's also worth noting that BitLocker uses a new encryption model in Windows 10 and 11 that might affect performance differently than in previous versions. If you continue to have issues, consider reaching out to Microsoft support for further assistance with your specific hardware setup.
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