SteamOS SSD, microSD, shader cache, and compatdata management

Scope

Storage optimization means recovering space or improving consistency without losing saves, prefixes, downloads, or a working rollback. Use Steam's Storage UI and normal uninstall/move paths first.

Do not run recursive delete commands copied from a forum against compatdata or shader directories. App IDs can be misidentified, and cloud sync does not protect every save or launcher state.

Baseline

Record free space, library locations, game/App IDs, installed size, shader/other category size shown by current UI, download state, save/cloud status, storage device model/capacity, filesystem health, and a repeatable load or traversal test when performance is the concern.

Change one variable

Use this order: finish/pause downloads, remove unsupported recordings/screenshots, uninstall unused content through Steam, move a game between libraries, then investigate one App ID's shader or compatdata state only for a documented fault. Never delete multiple unknown App-ID directories as a batch.

Measurements

GoalBefore/after evidenceAcceptance
Recover space
UI category and filesystem free space
Expected amount, no missing saves
Compare SSD/microSD
Same game/build and scene
Load/streaming result exceeds variance
Rebuild shader state
First and subsequent runs
Stutter/download cost recorded
Rebuild prefix
Launch, saves, launcher, controls
All required state restored

Side effects

Moving content consumes time and writes; microSD random I/O can affect some workloads; deleting shader data causes redownload or compilation and temporary stutter; rebuilding a prefix removes dependencies and local state; nearly full filesystems can worsen updates and rollback reliability.

Rollback

Restore saved game/prefix data to the same App ID, move the game back through Steam, reinstall removed content, allow shader processing to complete, and verify saves before deleting backups. If storage errors appear, stop writes and preserve data before filesystem repair.

Media selection

Valve supports UHS-I Class 3 or better microSD cards and notes that Deck does not use the higher UHS-II/III transfer rates. For SSDs, choose the exact physical format, power/thermal fit, capacity, firmware/support, and model-specific replacement procedure; interface labels alone do not prove compatibility.

Frequently asked questions

Is compatdata only disposable cache?
Is compatdata only disposable cache?
No. A Proton prefix can contain registry state, launchers, dependencies, and saves that are not in Steam Cloud. Identify and back up the App ID before removal.
Should I buy UHS-II or UHS-III for higher Steam Deck speed?
Should I buy UHS-II or UHS-III for higher Steam Deck speed?
Valve says those cards are expected to work but their higher transfer rates are not supported by Steam Deck. Capacity, authenticity, sustained behavior, and warranty still matter.

Sources

Version history

  • 2026-07-15: Phase 5 safe storage, shader, and prefix workflow published.