KB5063878 Windows 11: Drives Vanish Under Heavy Writes—Pause Updates

Microsoft’s August cumulative (KB5063878) is making some SSDs and HDDs vanish mid‑write, and a patchwork of community testing, vendor responses and cautious guidance now makes a compelling case for pausing non‑urgent Windows updates and treating large, continuous file transfers as high‑risk until the situation is clarified. (support.microsoft.com)

Background / Overview​

Microsoft released the Windows 11 24H2 cumulative on August 12, 2025 — KB5063878 (OS Build 26100.4946) — as a security and quality rollup. The public KB entry lists the usual fixes and improvements and, at the time of release, did not include a known‑issue entry describing storage devices becoming inaccessible. (support.microsoft.com)
Within days, independent testers and hobbyist researchers reported a reproducible failure mode: during sustained, large sequential writes (commonly cited around the ~50 GB mark), some storage devices — both NVMe SSDs and some HDDs — stop responding to the OS, SMART/controller telemetry becomes unreadable, files in flight can become corrupted, and the drive may either recover after a reboot or remain inaccessible and require deeper intervention. Early hands‑on reproductions and community collations have converged on a similar symptom fingerprint, although the scale of the problem across the global install base remains unquantified. (techspot.com)
This article explains what happened, how the bug manifests, what vendors and Microsoft have said so far, who appears to be at higher risk, practical mitigations for home users and IT teams, and the longer‑term implications for update trust and OS‑firmware coordination.

---

What happened, in practical terms​

Timeline and the immediate signal​

• Microsoft published KB5063878 on August 12, 2025 as the August cumulative for Windows 11 24H2 (OS Build 26100.4946). The KB packaged the latest servicing stack and cumulative fixes. (support.microsoft.com)
• Soon after the rollout, administrators reported a separate deployment problem — an installation error (0x80240069) affecting WSUS/SCCM that Microsoft addressed with a known‑issue rollback for managed environments. That distribution regression and its patching are separate from the storage reports but show the update’s real‑world complexity. (windowslatest.com)
• Community testing surfaced a storage regression: under heavy sequential writes (examples: large game installs, archive extraction, cloning), drives can “disappear” from Windows and sometimes suffer irrecoverable metadata or partition corruption. Multiple independent testers reproduced similar behavior. (techspot.com)
• SSD controller specialist Phison issued a public statement acknowledging the industry‑wide effects of KB5063878 and KB5062660 and said they were reviewing impacted controllers and coordinating with partners. That confirmation is an important datapoint because it comes from a major controller vendor rather than just community reporting. (tomshardware.com)

The symptom fingerprint (what users actually experienced)​

• Drives vanish from File Explorer, Device Manager and Disk Management mid‑write.
• SMART/controller telemetry becomes unreadable or fails to respond to vendor utilities.
• Files being written at the time become partially written, corrupted, or entirely lost.
• In many cases a reboot reinitializes the controller and restores visibility; in other cases the drive remains inaccessible even after reboots and requires reformatting or vendor tools. (techspot.com)

---

Technical analysis: why heavy writes can trigger controllers​

Modern SSDs are complex systems with tight co‑ordination between host drivers and controller firmware. Several technical elements make large sequential writes a plausible trigger for a regression:

• Sustained high‑volume writes exercise caching, metadata updates and garbage collection in ways short bursts don’t. That opens different firmware code paths and longer‑lived state in the controller.
• Host memory cooperation mechanisms, such as the NVMe Host Memory Buffer (HMB), change how DRAM‑less drives rely on the host for caching. Small changes in host timing or HMB allocation policy can expose firmware race conditions in certain controllers.
• Controller firmware edge cases: if a firmware path cannot safely handle an unexpected sequence of commands or prolonged DMA traffic, the controller may lock up, stop responding to host commands, and present to the OS as “disappeared.” Rebooting the host or power‑cycling the drive forces a hardware reset that sometimes recovers the controller, which explains why reboots frequently restore visibility.

Community testing narrowed the most likely mechanism to a host‑to‑controller interaction under continuous heavy writes; that pattern makes the issue plausible as an OS-induced exposure of a firmware weakness rather than a sudden batch of coincidental hardware failures. However, causation across every model or controller family remains unproven — the correlation is strong but not yet exhaustively verified. (techspot.com)

---

Who appears to be affected (models, controllers and patterns)​

No vendor has yet published a single, definitive list covering every impacted model, but aggregated community tests and early reporting point to the following patterns:

• Drives using certain Phison controller families have been repeatedly flagged in reproductions and community collations, which likely contributed to Phison’s public engagement. (tomshardware.com)
• A mixture of NVMe and SATA SSDs across several vendors (Corsair, WD, Kioxia, SanDisk, ADATA, SK hynix, Crucial, XPG, Solidigm, and others) showed symptoms in distributed tests; many drives were recoverable after reboot, a minority were not. (ghacks.net)
• Community reproductions consistently cite sustained writes of approximately 50 GB or more and drives being >60% full as common triggering conditions, which aligns with how controllers and metadata management are stressed during large transfers. Two independent outlets that aggregated testing corroborate the ~50 GB sustained write trigger in multiple reproductions. (techspot.com) (pcgamesn.com)

Notably, some high‑end models (for example, certain Samsung 990 Pro configurations and several WD Black SKUs) have not shown the fault in the same tests, demonstrating that the regression is neither universal nor strictly brand‑specific. Community lists are evolving and have sampling bias toward enthusiast testers who run heavy workloads — they are investigative leads rather than formal vendor recalls.

---

Vendor and Microsoft responses so far​

• Microsoft: KB5063878 remains published and its public KB page initially showed no known storage regressions. Microsoft did acknowledge and mitigate the WSUS/SCCM installation error (0x80240069) for enterprise channels. That fix demonstrates Microsoft’s ability to use Known Issue Rollback (KIR) and servicing controls for distribution issues, though at the time of early reporting Microsoft had not added an explicit “storage‑disappearance” known issue to the KB entry. (support.microsoft.com) (windowslatest.com)
• Phison: publicly acknowledged industry‑wide effects linked to KB5063878 and KB5062660 and said they are reviewing controllers that may have been affected and coordinating with partners. That statement raises the issue beyond community rumor because it signals a major SSD controller vendor is engaging on a potential host‑triggered regression. (tomshardware.com)
• Other SSD vendors: as of early reports there was no single consolidated bulletin from every major SSD vendor listing every affected model; several vendors and enthusiast outlets were nevertheless investigating and communicating model‑specific guidance via dashboards and support channels. Community aggregates caution users to check vendor tools and advisories continuously.

Important caveat: vendor and Microsoft public statements are evolving. Until vendors publish firmware advisories or Microsoft documents a known issue specific to storage, the causal chain cannot be closed with absolute certainty.

---

Practical guidance: what to do right now (home users and power users)​

This is actionable, conservative advice based on community reproductions, vendor commentary and standard storage safety practice.

• Back up now. If you installed KB5063878 and a drive shows any sign of instability, back up all accessible data immediately to an independent physical device or cloud. Backups are the only reliable protection against in‑flight write corruption.
• Avoid large, continuous writes on recently patched systems. Postpone bulk transfers (game installs/updates, large archive extractions, cloning, VM image writes, video exports) until vendors or Microsoft publish mitigations. Community tests point to sustained writes ≈50 GB as the most reliable trigger. (pcgamesn.com) (techspot.com)
• If you haven’t installed KB5063878 yet and you rely on heavy I/O, consider pausing the update for a short period. Use Windows Update → Pause updates (consumer) or WSUS/SCCM staging (enterprise). Staging updates in a test ring and validating heavy‑write workflows is the prudent path.
• Check vendor tools and firmware. Run your SSD vendor’s dashboard or CrystalDiskInfo to capture SMART and firmware revision. If the vendor publishes a firmware patch for your exact model, follow their instructions — but make a verified backup first. Firmware flashes carry risk and should be applied carefully.
• If a drive disappears mid‑write: stop further writes, capture Event Viewer logs (Windows Logs → System) and vendor diagnostics, and image the drive to a different device before attempting repairs. Rebooting may restore visibility but can also overwrite metadata and complicate forensic recovery. If data is critical, seek professional recovery rather than amateur "fixes."

Short checklist (ordered):

• Back up accessible files now.
• Pause large I/O jobs on patched systems.
• Inventory drives and firmware versions.
• Apply vendor firmware only after backups and vendor guidance.
• Report failures to Microsoft Feedback Hub and vendor support with logs.

---

Guidance for IT administrators and enterprises​

Enterprise deployment needs to balance security patching against operational risk. Recommended actions:

• Stage the update: Hold KB5063878 in a preproduction ring until you can validate against representative storage hardware and heavy‑write workloads in your fleet. Use WSUS/SCCM blocks or KIR controls as appropriate.
• Inventory endpoints: Identify systems with at‑risk controllers (community lists point to Phison families and some DRAM‑less designs) and prioritize testing on those devices.
• Run sustained write tests: Simulate the ~50 GB+ sequential writes that triggered community reproductions. Capture telemetry, event logs and vendor diagnostics if failures occur.
• Keep backups off the same potentially affected models: Ensure backup targets are on drives/arrays that are not using the same suspect SSD models. Imaging and redundancy protect against platform‑level regressions.

---

Recovery: what to do if a drive fails​

• If the drive becomes inaccessible but you can still see the device, create a bit‑for‑bit image to a known good target before any repair attempts. Imaging preserves recoverable sectors and prevents in‑place writes that reduce recovery chances.
• If the drive no longer appears, capture host logs and vendor diagnostics if available. Avoid repeated reboot cycles once you have the evidence.
• If vendor tools can access the controller in a diagnostic mode, follow vendor guidance; some firmware resets or fixes may restore the drive. If the drive remains inaccessible and data is critical, consider professional data recovery — ad hoc filesystem fiddling can make recovery harder.

---

Risk assessment: scope, severity and uncertainty​

• Severity: the impact is high where it occurs — data corruption and inaccessible drives are severe outcomes. Enough independent reproductions and a controller vendor statement (Phison) elevate the issue beyond rumor. (tomshardware.com)
• Scope: the prevalence across the entire Windows 11 install base is uncertain. Community testing is biased toward enthusiasts who run heavy writes; normal desktop users may never trigger the workload profile that exposes the fault. That said, gamers, creators, and IT departments that perform large backups or cloning are more exposed.
• Root cause: plausible but unconfirmed. Evidence points to an interaction between host changes (the Windows update) and vulnerable controller firmware under sustained writes, but formal vendor/Microsoft telemetry is required to definitively attribute causation. Until coordinated diagnostics arrive, treat model lists as investigative rather than authoritative.

Flagging unverifiable claims: some early headlines used dramatic language like “bricking” or “destroying” drives. While worst‑case reports exist, the majority of documented reproductions show temporary disappearance recoverable by reboot; permanent data loss appears to be a minority outcome so far. Those worst‑case reports must be treated as high priority and investigated, but they do not prove universal hardware destruction.

---

Why this matters beyond a single update​

• Update trust: when a security rollup introduces a host‑level regression with potential data loss, users and administrators face a dilemma — install promptly to stay secure, or delay to avoid hardware risk. That trade‑off erodes immediate update trust and complicates patch management.
• OS‑firmware coupling: modern storage relies on tight cooperation between OS drivers and firmware. Host changes (timing, HMB policy, I/O path changes) can reveal latent firmware bugs. The episode underscores the importance of coordinated pre‑release testing matrices between OS vendors and SSD makers.
• Operational exposure: enterprises that perform bulk migrations, backups, or VM provisioning must include heavy‑write scenarios in testing rings; failing to do so leaves fleets exposed to a class of bug that only shows up under stress.

---

Bottom line and final recommendations​

• Short term: back up now and avoid large continuous file transfers on systems that installed KB5063878 until vendors or Microsoft publish explicit guidance or remediation. If you haven’t installed the update and your workload involves heavy writes, defer the update temporarily and stage it against representative drives.
• Monitor vendor dashboards and Microsoft Release Health for firmware advisories or known‑issue updates; if a vendor issues a firmware patch for your exact model, follow their update path after securing backups. (tomshardware.com)
• For IT teams: inventory, stage, test, and use WSUS/SCCM policies to block or stagger the rollout until you can validate heavy‑write workflows on representative hardware.
• Maintain perspective: community reproductions and vendor statements are a strong early signal that this is a real risk for specific workloads and hardware; the problem is plausible and actionable, but the full scope and definitive root cause require coordinated vendor and Microsoft telemetry to be finalized. Treat current model lists and anecdotal outcomes as evolving evidence rather than settled fact. (techspot.com) (tomshardware.com)

This episode is a sharp reminder that updates change low‑level host behavior and that backups remain the single best defense against unexpected platform regressions. Protecting data, staging updates, and prioritizing vendor‑backed fixes are the pragmatic strategies until the underlying interaction is conclusively diagnosed and fixed.

---

Conclusion
The KB5063878 situation is a live, evolving incident: community testers reproduced a clear, high‑risk failure profile during sustained writes, Phison has publicly acknowledged industry‑wide effects, and Microsoft has already acted on a separate WSUS install issue — all of which justify a cautious approach. Short‑term restraint (back up, pause large writes, stage updates) is a small operational cost compared with the potential for unrecoverable data loss. Continue to watch vendor advisories and Microsoft release health for definitive remediation steps and, in the meantime, prioritize backups and staged testing for any device used for large, sequential I/O. (tomshardware.com)

---

Source: Windows Central Should you hold off on Windows updates? This SSD bug makes a strong case