A Dev Drive is a ReFS volume built for repos, package caches and build output. When it is marked trusted, Microsoft Defender runs in performance mode on it instead of full real-time scanning. You get faster builds and take on responsibility for what you store there.
What a Dev Drive is
Microsoft describes Dev Drive as storage for key developer workloads, using ReFS with targeted optimisations and more control over trust, antivirus configuration and attached filters. It is meant for source repositories, package caches, and build output and intermediate files.
It is not for installing applications, and the C: drive cannot be a Dev Drive. Existing volumes cannot be converted: the designation happens at format time, and reformatting destroys the content.
Prerequisites in short
- Windows 11 build 10.0.22621.2338 or later.
- 16 GB memory recommended, 8 GB minimum.
- At least 50 GB free disk space.
- Local administrator permissions.
Trusted versus untrusted
New Dev Drives are designated trusted at format time. Trusted is the signal for Defender to use performance mode. Microsoft says real-time protection must still be on for performance mode to apply, and that real-time protection continues on all other volumes.
An untrusted Dev Drive does not get that privilege and is scanned in real-time protection mode. Microsoft's guidance is to use the default performance mode setting only on a trusted drive and to be careful about granting trust after creation.
Check status with:
fsutil devdrv query D:
The risk you accept
Microsoft frames this as a trade between performance and security, and compares it to adding an exclusion in Windows Security. You take on responsibility for the content stored on the drive.
A repo you cloned from an unknown source, or an archive you extracted, is exactly the content you may not want to treat as trusted. One practical approach is a separate untrusted volume for experiments and a trusted one for projects you already vet.
Dev Drives can also run with no antivirus filter attached. Microsoft warns to exercise extreme caution and says removing antivirus filters is a security risk.
Moving a drive
Trust is per machine. A VHD copied to another machine is treated as an ordinary volume until you mark it trusted there. Microsoft does not recommend copying a VHD to a different machine and continuing to use it as a Dev Drive.
Practical rules
- Keep real projects you vet on the trusted drive.
- Do not put downloaded installers or unknown archives there.
- Do not detach antivirus filters to save a few seconds.
- Keep BitLocker on the host volume. Microsoft says a Dev Drive VHD is covered by BitLocker on its hosting volume.
- Scan your dependencies regardless of where the files live. Safeguard's free scan at gold.safeguard.sh/scan works on a repository.
Quick check
Can I convert my existing D: drive to a Dev Drive?
No. Microsoft says existing volumes cannot be converted. The designation is made at format time, and reformatting destroys content.
Does performance mode turn Defender off?
No. It is a Defender capability with real-time protection on, which reduces scan impact on a trusted Dev Drive.
Sources
Last reviewed: 19 October 2026.
