Microsoft released Dev Drive at the Build 2023 developer conference, a custom storage volume geared for developers. Built on top of Microsoft's proprietary ReFS (Resilient File System), Dev Drive is optimized for heavy I/O operations and has improved performance and security capabilities.
Dev Drive includes file-system optimizations and Microsoft claims up to 30% improvement in build times as well as improved security using the new performance mode in Microsoft Defender for Antivirus. In Microsoft Defender performance mode, real-time protection runs asynchronously, balancing security and performance. The balance is reached by delaying security scans until after the file operation has been completed instead of running security scans synchronously while the file operation is being executed. This performance mode is more secure than a folder or process exclusion that disables security scans altogether.
Dev Drive also speeds up other disc-bound operations such as cloning Git repositories, restoring packages, and copying files. Dev Drive is designed for storing source code, package caches and build artifacts but it is not intended for developer tools or installing apps.
Another optimization that Dev Drive implements is copy-on-write (CoW) linking, also known as block cloning. The article on Engineering@Microsoft describes how it works:
Copy-on-write (CoW) linking, also known as block cloning in the Windows API documentation, avoids fully copying a file by creating a metadata reference to the original data on-disk. CoW links are like hardlinks but are safe to write to, as the filesystem lazily copies the original data into the link as needed when opened for append or random-access write. With a CoW link you save disk space and time since the link consists of a small amount of metadata and they write fast.
Dev Drive is currently in public preview and is available to Windows Insiders running the Dev Channel of Windows 11. It requires at least 50GB in free space and a minimum of 8GB of RAM though Microsoft recommends 16GB. Users can create a Dev Drive volume as a new virtual hard disk, or it can use unallocated space.
Those developers who already tried the Dev Drive report getting faster builds, with one user seeing about 40% off npm build and about 20% speedier .NET build. Another user got 25% speed up even though Dev Drive was running on a three-times slower disk.
Dev Drive should appear in the main Windows release channel later this year. It will also be available in Azure Pipelines and GitHub Actions for faster CI builds in the cloud. In addition to the original release blog post, Microsoft has published a detailed page that describes how to set up Dev Drive, what limitations it has as well as frequently asked questions.