Should the second SSD be a Dev Drive? What can only be decided at format time, and what it trades away
If a second SSD is going into a machine used for development, Windows 11 offers a choice an ordinary volume does not: Dev Drive. It is built on ReFS and hands control of volume settings and security, antivirus configuration included, to the person using it. One constraint dominates the decision: existing volumes cannot be converted. Microsoft states that the Dev Drive designation happens only at the original format time. This guide was written on 2026-09-21 from Microsoft's page and covers the prerequisites, the setup choices and the security trade. Nothing was benchmarked.
Published · Updated · FaultNote editorial policy
Who this guide is for and what to prepare
- People about to add a second SSD who are deciding whether to set part of it aside for development
- People who have seen Dev Drive in Settings and want to know how it differs from an ordinary volume
- People who want to understand the security position before turning it on
What you need
- Check the Windows version and build (Settings > System > About, or winver)
- Check installed memory and free space on the target drive
- Confirm you can sign in with local administrator rights
1. What a Dev Drive is, and how it differs
Microsoft's page opens with the definition: Dev Drive is a new form of storage volume available to improve performance for key developer workloads. Dev Drive builds on ReFS technology to employ targeted file system optimizations and provide more control over storage volume settings and security, including trust designation, antivirus configuration, and administrative control over what filters are attached.
A volume on ReFS with file-system optimisations, plus control over trust designation, antivirus configuration and which filters attach. That last part is the difference from an ordinary NTFS volume.
The scope is drawn just as plainly: a warning on the page states Dev Drive is intended only for key developer scenarios. It is not presented as a general-purpose fast volume, and this guide will not recommend it as one for video editing or photo libraries.
2. It can only be decided when the volume is created
This is what makes it a pre-purchase decision: Existing storage volumes cannot be converted to be a Dev Drive. The Dev Drive designation happens only at the original format time.
There is no switching an SSD over while keeping what is on it. The decision belongs to the plan — adding a second drive, or carving out unallocated space — not to a later change of mind.
The prerequisites are listed on the same page.
Scroll horizontally to see the full table →
| Prerequisite | As stated by Microsoft |
|---|---|
| Windows version | Windows 11, Build #10.0.22621.2338 or later |
| Memory | Recommend 16 GB (minimum of 8 GB) |
| Free space | Minimum 50 GB |
| Edition | Available on all Windows SKU versions |
| Permissions | Local administrator permissions |
| Managed environments | A security administrator must configure Dev Drive security policy |
3. Partition or VHD
Three options are offered at creation: build on a new virtual hard disk, resize an existing volume to make unallocated space, or use unallocated space that already exists. The real decision is between a partition on the physical disk and a virtual hard disk.
Microsoft sets out both sides. A partition generally offers faster performance because it directly uses the physical disk without any additional layers, with the trade-offs that resizing partitions can be more complex and risky and that the partition is tied to the physical disk. A VHD may have slightly lower performance due to the overhead of managing the virtual disk layer, but offers more flexibility for dynamic resizing, moving or backing up data, and is highly portable.
One caveat sits underneath that portability: when a VHD is hosted on a fixed disk (HDD or SSD), it is not recommended to copy the VHD, move it to a different machine, and then continue using it as a Dev Drive. Portable is not the same as recommended to move.
If you choose a VHD, the minimum size is 50 GB, and Microsoft recommends a per-user directory path for the file to avoid unintentional sharing.
Scroll horizontally to see the full table →
| Option | Advantage Microsoft states | Trade-off Microsoft states |
|---|---|---|
| A disk partition | Generally faster, using the physical disk directly without additional layers | Resizing is more complex and risky, and it is tied to the physical disk |
| A new VHD | More flexible for resizing, moving and backing up, and highly portable | Possibly slightly lower performance from the virtual disk layer |
4. What the speed is traded against
This is the section that matters most. The performance comes with control over security handed to the person using the volume, and Microsoft says so directly: Typically, there is a tradeoff between performance and security. Using a Dev Drive places control over this balance in the hands of developers and security administrators.
The default is not what people often assume. Antivirus filters, including both Microsoft Defender and 3rd-party antivirus filters, are attached to a Dev Drive by default. On top of that, Microsoft Defender Antivirus defaults to the new performance mode setting on Dev Drives, described as taking speed and performance into account while providing a secure alternative to folder exclusions. A Real-time protection mode is also offered for an increased level of protection.
Trusted has a specific meaning here. Dev Drives are automatically designated as trusted using a flag stored in the system registry during the original formatting time, and a trusted Dev Drive means that the developer using the volume has high confidence in the security of the content stored there. The page compares it to adding an exclusion in Windows Security: the developer takes on responsibility for managing the security of the content in exchange for performance.
And there is a warning: Dev Drives can be run with no antivirus filters attached. Exercise extreme caution! Removing the filters is described as a security risk that leaves the drive outside standard security scans, and Microsoft recommends the default performance mode on a trusted Dev Drive. This guide gives no procedure for detaching filters.
One more practical point: any product or feature requiring additional filters will not work unless the filter is added to the Dev Drive. If you run backup or monitoring software, check that before committing a volume.
5. Deciding how to divide the second SSD
Turning the above into a plan for the drive you are about to buy:
Nothing here was measured. Microsoft's page points at a blog post for average improvement figures across common developer operations; this guide does not quote them. What it does on your machine can only be found by creating one and timing your own work.
Scroll horizontally to see the full table →
| What the second SSD is for | Does Dev Drive apply | Why |
|---|---|---|
| Source code, package caches, build output | Yes | These are the developer workloads the page names |
| Installing games | No | The page states it is intended only for key developer scenarios, not as a general fast volume |
| Photos, video, documents | No | Same reason, and trust designation means taking responsibility for the content on that volume |
| Converting the SSD you already use | Not possible | Existing volumes cannot be converted; the designation happens only at format time |
| Trying it on a work-issued PC | Check first | In a managed environment a security administrator has to configure Dev Drive security policy |
Limitations and requirements
- Existing volumes cannot be converted, so this involves formatting. Make certain the target drive holds nothing you need.
- No procedure for detaching antivirus filters is given here. Microsoft itself warns to exercise extreme caution and states that the drive would fall outside standard security scans.
- Products and features that need additional filters will not work on a Dev Drive unless the filter is added. Check backup and monitoring software before committing a volume.
- The wording quoted was read on 2026-09-21. The prerequisite build number in particular can be revised.
Frequently asked questions
Can I convert the SSD I already use into a Dev Drive?
No. Microsoft states that existing storage volumes cannot be converted and that the Dev Drive designation happens only at the original format time. It is decided when a volume is created.
Will a Dev Drive make everything faster?
That is not what the page says. It positions Dev Drive for key developer workloads, not as a general-purpose fast volume. Nothing was measured for this guide, so no figure is quoted.
Does it turn antivirus off?
Not by default. Microsoft states that antivirus filters, both Defender and third-party, are attached by default, and that Microsoft Defender Antivirus defaults to performance mode on a Dev Drive. Filters can be detached, but the page attaches an explicit warning to doing so.
Partition or VHD?
Microsoft gives both sides: a partition is generally faster with no additional layers but is harder to resize and tied to the disk; a VHD is more flexible and portable but may be slightly slower because of the virtual disk layer. Choose by use.
How much space does it need?
The prerequisites give a minimum of 50 GB free disk space, and the minimum size for a VHD is also 50 GB. Memory is 16 GB recommended, 8 GB minimum.
Sources and verification date
Sources checked: . These sources support the specifications, procedures or prices discussed here. Check each source for applicable conditions and current information.
Related practical guides
- How much SSD does a gaming PC need? Windows requirements, published game sizes, library placement
- Before you buy a second SSD: the M.2 slots on your board are not interchangeable
- PCIe 4.0 or 5.0 SSD for gaming? Check load times, capacity and slot sharing
- SSD Endurance (TBW) and Warranty: Compare Write Limits of Popular NVMe SSDs by Capacity and Check Wear in Windows
- TLC vs QLC and DRAM vs DRAM-less (HMB): reading post-SLC-cache write speed off the datasheet
- M.2 SSD heatsinks: clearance, warranty terms and the PS5 requirement decide bundled or bare