---
title: "Move Windows build IO onto a Dev Drive"
description: "On Windows runners, put build output, caches and temp files on a Dev Drive."
url: https://starsling.dev/ci-playbooks/techniques/dev-drive-io
canonicalUrl: https://starsling.dev/ci-playbooks/techniques/dev-drive-io
---

# Move Windows build IO onto a Dev Drive

On Windows runners, put build output, caches and temp files on a Dev Drive.

## How to choose an approach

This technique currently has one documented company example. Validate its prerequisites, tradeoffs and original CI environment against your repository before adapting it.

- **[OpenAI](https://starsling.dev/ci-playbooks/openai#dev-drive-io)**: Use it when Windows build and test steps run much slower than the same steps on Linux and are heavy on file IO. Check before adopting: Creating the drive adds setup time to each job, and a single run is noisy; compare several runs on the same runner type.

## Apply this technique

````text
Evaluate and apply this CI technique to my repository: Move Windows build IO onto a Dev Drive.

On Windows runners, put build output, caches and temp files on a Dev Drive.

Read the technique and its source-backed company examples: https://starsling.dev/ci-playbooks/techniques/dev-drive-io.md

Inspect this repository’s CI workflows, build and test commands, dependencies, and recent run timings. Identify where this technique applies and explain the expected benefit using this repository’s evidence.
Measure a baseline from recent comparable runs: elapsed time, queue time, runner minutes and failures where available. If data is unavailable, say what cannot be measured.
Compare relevant company approaches, checking prerequisites, platform differences and tradeoffs. Rank applicable options by evidence, fit and measurable opportunity; do not present company results as predictions for this repo.
Recommend the smallest safe change, show what checks and fallback paths remain, and ASK ME WHICH CHANGE TO APPROVE BEFORE EDITING ANY FILES.
Only after approval, work on a new feature branch, make one reversible change, and open a reviewable pull request. Never merge or push to a default or protected branch.
Keep required checks, test coverage, deployment and release behavior intact. Validate the change and compare equivalent runs where possible; report limitations and what should be monitored after merge.
````

## How OpenAI used this technique

Read what OpenAI changed and follow the original sources.

### OpenAI: Move Windows build IO onto a Dev Drive

Codex routes its Cargo and Bazel build and cache directories through one CI build root. On Windows that root is a Dev Drive, and the Bazel output base moves there too.

Evidence: Single-run demonstration

The PR reports these timings from two refreshed shards whose tests failed, so it calls them directional. Traced Bazel test step on a cold cache: shard 1 16m22s to 12m05s, shard 3 16m48s to 11m08s, one sample each ([Source](https://github.com/openai/codex/pull/31357))

Use it when: Windows build and test steps run much slower than the same steps on Linux and are heavy on file IO.

Before applying it: Creating the drive adds setup time to each job, and a single run is noisy; compare several runs on the same runner type.

[Read more in the OpenAI playbook](https://starsling.dev/ci-playbooks/openai#dev-drive-io)

[Primary source](https://github.com/openai/codex/pull/31357)

## CI optimization is continuous work.

Apply this technique yourself, or use StarSling Runners for faster GitHub Actions and optional agent-driven optimization PRs, which teams on eligible paid plans can turn on.

[Get self-improving CI](https://starsling.dev/products/runners)

## Company Playbooks

### [Anthropic](https://starsling.dev/ci-playbooks/anthropic)

Run only affected tests

### [DoorDash](https://starsling.dev/ci-playbooks/doordash)

Run build and test in parallel, sharded across CI agents

### [Linear](https://starsling.dev/ci-playbooks/linear)

Benchmark the same job on faster hardware

### [Mastra](https://starsling.dev/ci-playbooks/mastra)

StarSling runners for the slowest test workflow

### [OpenAI](https://starsling.dev/ci-playbooks/openai)

Rank CI fixes by the minutes they save

### [Ramp](https://starsling.dev/ci-playbooks/ramp)

Move a CPU-bound test suite to a faster CPU

### [Shopify](https://starsling.dev/ci-playbooks/shopify)

Let an agent iterate against one CI metric

### [Spotify](https://starsling.dev/ci-playbooks/spotify)

Build arm64 on native arm64 runners

### [Stripe](https://starsling.dev/ci-playbooks/stripe)

Run only the tests a change can reach

### [Uber](https://starsling.dev/ci-playbooks/uber)

Build the merge-queue speculations most likely to be needed