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Summary
WSL 2 的 ext4.vhdx 虛擬硬碟採用動態擴充機制，刪除資料後不會自動回收空間。本文說明如何透過兩種方式壓縮：Hyper-V 的 Optimize-VHD（Windows Pro/Enterprise）或 diskpart（通用方法），並附帶 .bat 自動化腳本和 wsl --export/import 的替代方案。
WSL 2’s ext4.vhdx dynamically expands but never auto-reclaims space after deletion. This article covers two compression methods — Optimize-VHD (requires Hyper-V) and diskpart (universal) — plus a .bat automation script and wsl --export/import as a nuclear option.
Key Points
- WSL 2 virtual disk only grows, never auto-shrinks — requires manual
compactafter deleting large amounts of data (e.g., Docker images). - Step 1: Clean inside WSL first —
docker builder prune -a,apt-get clean/autoremove,npm/yarn cache clean, thensudo fstrim -v /to mark freed blocks. - Step 2: Shut down WSL completely —
wsl --shutdown— before touching the .vhdx file. - Method A (Hyper-V, Windows Pro+):
Optimize-VHD -Path <path> -Mode Full - Method B (universal):
diskpart→select vdisk→attach vdisk readonly→compact vdisk→detach vdisk - Nuclear option:
wsl --export→wsl --unregister→wsl --importcreates fresh minimal .vhdx. - A ready-to-use
CompactVHDX.batscript is provided in the article.
Insights
The fstrim step before compacting is critical and often missed — without it, the filesystem doesn’t mark freed blocks as available, so compact vdisk recovers nothing. The readonly mount during compaction prevents corruption. The Docker use case is common: every docker pull and failed build layer expands the .vhdx, but docker system prune only frees space inside the filesystem, not the .vhdx itself.
Connections
Raw Excerpt
WSL 2 的虛擬硬碟採用動態擴充機制，它會隨著寫入資料而變大，但在刪除資料後不會自動釋放空間回 Windows 系統，因此必須手動執行壓縮 (Compact) 操作。