Windows 11 24H2 KB5063878 Causes NVMe SSDs to Vanish Under Heavy Writes

Microsoft's August cumulative update for Windows 11 (KB5063878, OS Build 26100.4946) has been linked in community reports to NVMe SSDs becoming inaccessible after sustained, heavy file writes — an issue that has reopened concerns about storage stability in the 24H2 branch and forced a cautious response from power users and administrators. (support.microsoft.com)

Background / Overview​

Microsoft released KB5063878 on August 12, 2025 as a security-and-quality cumulative update for Windows 11 (24H2), packaged with a servicing stack update (SSU). The official update notes show the release date, the OS build (26100.4946) and list general fixes and improvements; Microsoft’s published page currently lists no known, acknowledged issues for this update. (support.microsoft.com)
Within days of the rollout, however, independent reports — amplified by social posts from storage enthusiasts and a Japanese PC builder — described a reproducible failure mode: during continuous file transfers of roughly 50 GB or more, certain NVMe SSDs would stop responding, disappear from the OS device list, and present unreadable SMART data; a reboot restored temporary visibility but not reliability, and some users reported file corruption on volumes that experienced the fault. These community reports were summarized by technology outlets and forum threads and picked up by Notebookcheck’s coverage of the issue. (neowin.net)
This is not the first time the Windows 11 24H2 family has shown storage-related regressions: earlier interactions between Host Memory Buffer (HMB) behavior, Microsoft’s storage stack changes, and certain DRAM‑less or Phison‑based controllers produced instability in late 2024 and 2025. Those previous episodes set the context for alarm — both for their technical similarity and because firmware/OS coordination is often required to safely resolve such problems.

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What the reports say — symptoms, scope, and affected models​

Symptoms reported by users​

• SSDs disappear from Windows Device Manager during or immediately after sustained writes (reported threshold commonly ~50 GB).
• The drive’s SMART and controller attributes become unreadable by the OS while the fault persists.
• A reboot usually restores drive visibility temporarily, but the instability can recur under similar workloads and in some cases produce file system corruption.
• Not all drives behave the same; some users reported that certain models recover after reboot while others remain inaccessible or show corruption.

Reported model list (community-collected)​

Per community reports collated in technology writeups and forum threads, examples of drives implicated in early reports include:

• Corsair Force MP600 (Phison E16 controller)
• Phison PS5012‑E12 reference boards
• SanDisk Extreme Pro M.2 NVMe (Triton MP28 controller)
• Fikwot FN955 (MAP1602 + WDS X3 9070 controllers)
• Kioxia Exceria Plus G4 1 TB (Phison E31T)
  Additional models mentioned in follow-up posts (some recover after reboot): WD Blue SN5000, WD Red SA500 SATA, Corsair MP510, Crucial P3 Plus. These lists were drawn from independent community testing and roundups and have not been officially validated by Microsoft or the drive vendors as a single, confirmed compatibility list.

How widespread is this?​

At the time coverage began, public reports remained modest in volume — fewer than widely distributed update disasters — but were consistent enough to trigger close attention from enthusiasts and admins. Outlets that aggregated the reports emphasize that the failure pattern is predictable under heavy sustained writes in affected configurations, yet not all systems or models reproduce the behavior. Independent reporting stresses that Microsoft and most SSD manufacturers had not issued a unifying confirmation when these stories first circulated. (neowin.net)

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Technical analysis: plausible causes and limits of current knowledge​

What’s plausible — HMB, controller firmware, and OS buffering​

Experienced storage diagnosticians point to a few recurring technical themes that fit the reported symptoms:

• Host Memory Buffer (HMB) and driver interactions. Prior 24H2 incidents were caused by changes in how Windows allocates HMB for DRAM‑less SSDs; the OS-level allocation interacting with certain controllers and firmware produced BSODs and instability. That earlier pattern demonstrated how an OS change can push a drive’s controller into an unexpected operating region. The current reports echo that interaction, though they do not uniformly identify HMB as the root cause.
• Controller firmware behavior under sustained writes. The symptom set — drives becoming unresponsive during heavy continuous writes and SMART attributes becoming unreadable — is consistent with a controller or firmware fault under high sustained IO or with a cache-flushing path that fails to complete. Phison controllers have been singled out in multiple independent posts, which is unsurprising because Phison’s controllers are widely used across many brands and because specific firmware revisions have historically shown edge‑case instability under stress. Still, not all affected drives use Phison controllers, so the controller family alone does not fully explain the reports. (neowin.net)
• OS-level buffered cache or memory leaks. Another hypothesis raised by commentators is that a Windows-side kernel buffering or cache subsystem regression under specific workloads causes the stalling or miscommunication with the NVMe driver, triggering a controller timeout and drive disappearance. This would match the pattern where a reboot temporarily restores visibility but the underlying problem recurs. This theory remains speculative pending vendor-level analysis. (neowin.net)

What is not verified​

• There was no immediate, official statement from Microsoft or a single SSD vendor acknowledging that KB5063878 specifically causes permanent drive failures across a defined set of models at the time these community reports surfaced. The update’s official page lists no known issues and provides routine guidance for installing or removing the LCU/SSU components. That lack of confirmation means some online claims remain unverified. Administrators should treat early community lists as investigative leads, not definitive recall notices. (support.microsoft.com)
• Precise failure thresholds (for example, “exactly 50 GB of continuous writes”) are community-observed patterns rather than hardware-provided limits; different drives and system configurations can show varied behavior. Treat the numbers as indicative patterns, not absolute technical specifications.

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Strengths and risks in the response so far​

Strengths​

• Microsoft’s KB page confirms the update and the build; the company bundles SSU and LCU with documented uninstall guidance for administrators — a necessary control for enterprise remediation. That page is the authoritative reference for what the update contains. (support.microsoft.com)
• Community reporting includes reproducible test conditions and model lists that help narrow the problem to specific controller families, workloads, and firmware combinations. These grassroots diagnostics often accelerate vendor triage and produce actionable mitigation steps (for example, firmware updates or registry workarounds) before vendors publish formal advisories.

Risks and gaps​

• Lack of vendor confirmation: There was no consolidated statement from Microsoft or from the major SSD vendors that a single, verifiable bug in KB5063878 is officially the cause of permanent SSD failure. The absence of vendor validation increases the risk of overreaction or misattribution.
• Data‑loss potential: The worst‑case scenarios reported include file system corruption and drives that become inaccessible — outcomes that can cause permanent data loss if no backups exist. The presence of file corruption in user reports elevates this beyond a mere performance glitch.
• Incomplete sampling: Public reports may bias toward enthusiasts and professional users who run sustained transfers regularly; consumers with different usage patterns may never see the bug. That means measured incidence in forums underestimates or mischaracterizes enterprise exposure without a structured telemetry signal from vendors or Microsoft.

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Practical guidance — what to do now (consumer and IT admin checklists)​

The guidance below synthesizes community mitigation steps, Microsoft update mechanics, and standard best practices for storage safety. Where listed, actions are presented in short, practical steps.

Immediate consumer-level actions​

• Pause or delay installing KB5063878 if you have not yet installed it and you rely on an NVMe drive for important data or run sustained large transfers. Community reporting suggests caution until firmware/OS fixes are confirmed.
• If you already installed KB5063878 and see storage instability, stop heavy transfers immediately and check drive health with vendor tools (for example, manufacturer dashboards / CrystalDiskInfo / smartctl). Back up any at‑risk data from the drive while it remains accessible.
• If you observe drive disappearance or data corruption, do not repeatedly reboot hoping for recovery. Take an image backup (if feasible) or use vendor diagnostic tools to capture logs before further changes. Reboots may restore visibility but can mask the root cause and complicate forensic recovery.
• Check for firmware updates from your SSD vendor and apply them per vendor instructions; many stability issues have historically been resolved by firmware patches. If a vendor publishes a firmware advisory, follow their recommended update path and back up data before flashing.

IT administrator / enterprise actions​

• Inventory endpoints for at-risk devices. Prioritize systems using DRAM‑less NVMe SSDs, Phison controller families, or the specific models named in early reports and vendor advisories.
• Hold the KB push on exposed fleets until vendors and Microsoft publish firm guidance. Use WSUS/SCCM policy controls to pause or approve updates selectively. Note: KB deployment via WSUS/SCCM saw reported install errors (0x80240069) for some administrators during the KB’s rollout, so monitor WSUS logs closely. (windowslatest.com)
• Require firmware verification and updating prior to upgrade. Use vendor utilities in staged testing to confirm firmware versions that vendors have validated with Microsoft.
• If an emergency workaround is required, consider registry mitigation (HMB allocation policy edit) as a temporary measure only — it reduces performance and is not a long‑term fix. Community-discovered registry keys include HmbAllocationPolicy under storport/stornvme parameter locations; this approach was used in earlier 24H2 incidents to limit HMB allocation. Treat registry changes as emergency mitigations and document changes carefully.

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How to check whether KB5063878 is installed and how to remove it (concise steps)​

• To confirm the update and OS build on a Windows 11 device: open Settings → System → About, or run winver.exe to check the build (should show 26100.4946 for KB5063878). Microsoft’s KB page also documents the release and provides file listings and removal guidance for administrators. (support.microsoft.com)
• Microsoft notes that the combined SSU+LCU package cannot be removed via the simple wusa /uninstall mechanism because the servicing stack update is included; the LCU can be removed via DISM with the package name. Administrators should consult the update file information and follow Microsoft’s prescribed removal procedure rather than attempting ad hoc removals. (support.microsoft.com)
• Uninstall caution: removing cumulative updates or service stack packages can have dependencies and may disrupt system security posture. Escalate removal actions through your standard change control process and prefer vendor-recommended mitigations or firmware updates where possible. (support.microsoft.com)

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Vendor coordination and verification: what to watch for​

• Official advisories: Watch for consolidated advisories from Microsoft’s Windows release health dashboard and from SSD vendors (SanDisk, WD, Phison, Kioxia, Corsair, Crucial, etc.). Official firmware advisories or Microsoft-issued mitigations are the authoritative fix path. (support.microsoft.com)
• Firmware tool outputs: When vendors publish firmware updates, their dashboard tools will typically show pre‑ and post‑flash firmware revisions and any known fixes. Record these outputs for compliance and rollback planning. (neowin.net)
• Telemetry and logging: If you manage fleets, collect stornvme, storport, and kernel event logs from affected machines and share redacted technical logs with vendors or Microsoft support channels to accelerate root-cause analysis. Community threads that surfaced the issue emphasized the value of detailed reproduceable workloads and logs.

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Conclusion — calibrated caution, not panic​

The KB5063878 story is an important reminder that cumulative security updates — even when well‑intentioned and necessary — can interact in unexpected ways with complex hardware ecosystems. The early reports of SSDs becoming inaccessible during sustained writes are serious because they implicate possible data corruption and device instability; at the same time, community-collected model lists and symptoms remain investigative, not official recalls.
For everyday users and administrators, the right posture is calibrated caution:

• Delay applying KB5063878 broadly on systems with at‑risk storage until vendors and Microsoft provide confirmation or fixes.
• Prioritize backups, firmware verification, and staged testing for critical endpoints. (neowin.net)
• Treat registry HMB mitigations as emergency measures, not substitutes for vendor updates.

Continue to monitor Microsoft’s KB page for KB5063878 and the Windows release health dashboard for any official changes, and watch vendor support portals for firmware advisories. The community reporting has been valuable for early detection; final resolution will depend on coordinated vendor analysis, firmware fixes where required, or Microsoft mitigations that definitively address the root cause. (support.microsoft.com, neowin.net)

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Source: Notebookcheck Latest Windows 11 update reportedly triggers SSD failures during heavy file transfers