Windows 11 KB5063878: SSDs Disappear Under Heavy Writes

Microsoft’s August cumulative for Windows 11 (the KB5063878 rollup, OS Build 26100.4946) has been linked by independent testers and enthusiast outlets to a storage regression that can make some SSDs temporarily — and in a minority of cases permanently — disappear during sustained large writes, with multiple community reproductions pointing to a common trigger window around 50 GB of continuous writes.

Background / Overview​

Microsoft released the August 2025 cumulative update for Windows 11 24H2 as KB5063878 (OS Build 26100.4946). The rollup bundled security fixes and routine servicing changes, but within days of the public rollout several community testers reported a reproducible storage regression: when performing sustained, large sequential writes — commonly cited near or above 50 GB — some NVMe SSDs (and a few HDD reports) could stop responding and disappear from Device Manager, Disk Management, and File Explorer. Reboot sometimes restores visibility, but written files can be corrupted; in a small number of cases drives failed to reappear without reformatting or vendor-level intervention. (notebookcheck.net, guru3d.com)
Those early reports began with an X (Twitter) user conducting hands‑on tests and were subsequently covered by multiple specialist outlets and community threads that aggregated model lists, reproduction steps, and recovery notes. Coverage remains evolving; Microsoft has not published a storage‑specific Known Issue entry tied to this LCU at the time these community reports circulated, and several SSD manufacturers had not issued formal statements initially. (guru3d.com, techradar.com)

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What users and testers are reporting​

• Symptom fingerprint: mid‑write disappearance of an SSD from the OS topology (File Explorer, Disk Management, Device Manager), unreadable SMART/controller telemetry to vendor tools, and corrupted or missing files created during the failure window. Reboot sometimes restores the device but does not necessarily restore data integrity.
• Typical trigger: sustained sequential writes (large game downloads/updates, archive extraction, cloning, or mass file copies). Most community reproductions point to a threshold in the neighborhood of 50 GB of continuous writes and/or drives with utilization above ~60%. (notebookcheck.net, easeus.com)
• Affected hardware: community collations initially flagged SSDs using certain Phison controller families and many DRAM‑less designs, but subsequent tests show the phenomenon is not strictly limited to a single controller vendor or brand — examples in aggregated lists include drives from Samsung, Western Digital, Corsair, Crucial, SanDisk, and several OEM controller families. Reported models vary across testers and firmware levels. (guru3d.com, notebookcheck.net)
• Geographical concentration and evidence caveat: early clusters of reports originated in Japan and were widely shared through X (Twitter) and Japanese outlets, and much of the initial material used machine translation. That doesn’t invalidate the technical reproducibility reported by testers, but it reinforces the need for wider, independent confirmations and vendor telemetry.

These observations are consistent across several independent write‑ups and hands‑on reproduce attempts, and they form the basis for the practical guidance community outlets are giving to users until vendors or Microsoft publish authoritative diagnostics and fixes. (tomshardware.com, notebookcheck.net)

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Technical analysis: why a Windows patch can expose SSD edge cases​

Modern NVMe SSD reliability depends on complex interactions between OS host drivers, the NVMe command queue, controller firmware, and NAND management (cache, DRAM or Host Memory Buffer, wear leveling, and garbage collection). Under sustained sequential writes:

• Drive caching and controller metadata updates are stressed continuously.
• Host DMA traffic and kernel buffering patterns differ from typical desktop bursts.
• DRAM‑less drives that use Host Memory Buffer (HMB) rely on carefully timed host allocations and firmware assumptions.

A small change in the OS storage stack — timing, buffer behavior, or HMB allocation policy — can expose latent firmware race conditions or unhandled edge cases in SSD controller firmware. In such cases the controller can effectively “lock up” or enter an error state that the host perceives as a detached device. Historically, remediation for similar incidents has been a combination of firmware patches from SSD vendors and targeted host-side servicing.
Two technical mechanisms are worth highlighting because community evidence points to them as plausible contributors:

• Host Memory Buffer (HMB) allocation and timing. HMB exposes system RAM to DRAM‑less controllers; differences in when and how Windows allocates/reclaims HMB under heavy I/O could trigger a firmware bug in controllers that assume stricter timing semantics. Past Windows 11 interactions with HMB have produced drive-specific issues, and vendors have previously issued firmware fixes for similar symptoms.
• Controller cache exhaustion and metadata update races. Sustained writes push the drive’s internal garbage collection, mapping-table updates, and thermal/power management code into atypical states. If a firmware path mishandles a prolonged cache flush or encounters a resource starvation scenario (exacerbated by near‑full drives), the drive can stop responding until the controller undergoes a hardware reset. Community reproductions that note higher failure rates on drives with >60% used capacity support this hypothesis.

Both mechanisms point to firmware‑level vulnerabilities that an OS change can easily trigger — which means fixes will likely come as coordinated vendor firmware updates, Microsoft servicing changes, or both.

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Reproductions, scope, and limits of current evidence​

Multiple community testers have published step‑by‑step reproductions that converge on the same workload profile (large, continuous writes in the tens of gigabytes). One widely cited hands‑on thread reproduced failures across two dozen drives and reported a mix of transient and permanent outcomes; popular high‑capacity consumer models such as the Samsung 990 Pro and WD Black SN7100 were included among affected samples in community lists, although not every sample of a model failed. (tomshardware.com, notebookcheck.net)
Cross‑checking key claims with independent outlets shows consistent signals:

• Tom’s Hardware reported independent reproductions that matched the 50 GB trigger and noted a mix of recoverable and unrecoverable cases.
• NotebookCheck and Guru3D aggregated community lists and technical commentary pointing to Phison families and DRAM‑less designs as disproportionately represented. (notebookcheck.net, guru3d.com)

Important limitations and caveats:

• The sample sizes are small and biased toward enthusiast testers who can run repeated stress patterns; community lists are investigative, not exhaustive.
• Many reports began in a single country (Japan) and relied on machine translation early on, creating an initial language‑barrier risk for global confirmation.
• Vendor telemetry and Microsoft Release Health-level confirmation were not widely published at the time of the early writeups; that means the definitive scale, affected firmware revisions, and whether any devices truly experienced irreversible controller damage remain to be established. These points should be treated as unconfirmed until vendors or Microsoft publish coordinated diagnostics.

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Vendor and Microsoft response status (what has, and hasn’t, happened)​

• Microsoft: The KB entry for KB5063878 did not initially include a storage-specific known issue. Microsoft did acknowledge and mitigate a separate enterprise distribution problem (WSUS/SCCM error 0x80240069) for the same update and applied Known Issue Rollback (KIR) steps for managed environments. That WSUS install issue is a separate failure mode but demonstrates Microsoft’s active servicing controls for the August rollup.
• SSD vendors: At the time early reports circulated, most major SSD manufacturers had not issued broad public advisories specifically linking KB5063878 to SSD disappearances. Historically, vendors have released firmware updates when firmware edge cases were implicated by Windows changes, and community guidance recommended checking vendor tools for firmware updates and advisories. Some vendors did later publish targeted firmware fixes for related HMB/24H2 problems in earlier episodes, showing the typical remediation path.

Bottom line: community reporting moved fast; vendor and Microsoft telemetry and formal advisories can take longer because they must correlate device firmware IDs and failure telemetry. Treat the lack of a broad vendor statement as a current gap, not proof that the problem is fictitious.

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Practical guidance: what users should do right now​

The risk profile for this issue is high when it hits (possible data corruption or inaccessible partitions) but the absolute frequency across the Windows install base is unknown. The immediate, conservative measures below balance security‑patch hygiene against the risk of data loss.

• If you have NOT installed KB5063878 yet:
• Delay installing the update on machines where the primary drive is an NVMe/SSD used for large writes or where the drive contains critical, unbacked data.
• For enterprise admins, use WSUS/MECM (SCCM) staging policies to withhold the LCU from representative fleets until vendor confirmations arrive.
• If you have installed KB5063878:
• Avoid single continuous file transfers above ~50 GB on drives that are over ~60% utilized until vendor/Microsoft guidance is published. That is the operational trigger cited by multiple testers. (notebookcheck.net, easeus.com)
• Back up critical data immediately to external drives or cloud storage. Backup is the only fully reliable defense against write‑time corruption.
• Check your SSD vendor’s management utility for firmware updates and advisories; follow vendor instructions but only after backing up. Vendor firmware updates can fix controller bugs but can also carry their own risks; always have a backup before applying firmware.
• If you encounter a vanished drive:
• Stop performing writes to that system. Power down and collect logs/screenshots.
• Attempt a clean reboot; some users regained temporary visibility after reboot, which can help with imaging. Do not immediately reformat if data is valuable.
• Create a full image (forensics image) of the drive if possible before attempting recovery operations. Imaging preserves current state for vendor diagnostics and recovery attempts.
• Contact vendor support with model/firmware/SN and recovery images; they may provide a firmware or tool path.
• For power users and admins: run staged stress tests on representative hardware (simulating large writes) in a safe lab before wide deployment of KB5063878. This is the pragmatic approach used by enterprise teams when facing patch‑related uncertainty.

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Recovery and forensic notes (hands‑on)​

If a drive disappears mid‑write and remains inaccessible:

• Preserve evidence: avoid reformatting until you have an image or vendor guidance.
• Attempt a diagnostic boot from a Linux live USB to check whether the device enumerates differently at the host/NVMe layer; sometimes Linux-based tools can access the device where Windows cannot. In several community reports, low‑level reformat or partition overwrite from Linux was the only way to restore a drive that would not respond in Windows, but that often destroyed existing data — treat as last resort.
• Use vendor tools for SMART and firmware-level diagnostics; if SMART is unreadable, collect logs and contact vendor RMA/forensics. Vendors can often produce targeted tools or firmware reflash methods; they are the authoritative path for controller‑level fixes.
• For irrecoverable cases where data is mission‑critical, engage professional data recovery services that specialize in SSD controller forensics. These services are costly and success is not guaranteed, but they preserve the last best chance for retrieval when firmware corruption or controller failure has occurred.

Caveat: SSD recovery is fundamentally different and often more limited than HDD recovery due to encryption, wear‑leveling, and controller indirection; the earlier a system is imaged and vendor engagement occurs, the better the odds of recovering usable data.

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Risk assessment and long‑term implications​

This incident underlines two persistent realities for modern PCs:

• The Windows ecosystem must interoperate with an enormous variety of SSD controller firmware and hardware designs; even tightly tested updates can expose firmware edge cases that were not visible in pre‑release testing.
• For users and administrators the trade‑off between immediate security hardening (installing monthly rollups) and protecting against rare but severe compatibility regressions is real. The practical compromise is staged deployment, backups, and rapid vendor coordination when an edge case is discovered.

If the root cause proves to be a firmware edge case triggered by host behavior, expect the following remediation arc:

• Vendors identify impacted controller families and publish firmware updates for affected models.
• Microsoft issues guidance, and possibly a targeted servicing fix or Known Issue entry for KB5063878 if host behavior adjustments are needed.
• The Windows release‑health and vendor pages will be the authoritative sources for affected model lists and firmware revs; community lists are useful leads but not definitive.

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What remains unverified — and why that matters​

• Exact scale: There is no public, consolidated vendor/Microsoft telemetry enumerating how many drives were affected, what fraction recovered after reboot, or how many were permanently damaged. Community reproductions are technically credible but limited in scope. Treat prevalence estimates as provisional.
• Permanent hardware damage claims: A small number of community reports describe drives that did not return without reformatting or re‑initialization; whether these represent true irreversible controller failure or recoverable metadata corruption is a case‑by‑case forensic question that vendors must confirm. Until vendors publish forensics, permanent‑damage claims should be flagged as unverified.
• Single‑cause attribution: Early community lists over‑emphasized Phison families and DRAM‑less designs; subsequent postings show multi‑vendor involvement. The most defensible technical claim is that an OS-level change exposed firmware sensitivities under a narrow heavy‑write profile — not that any single vendor or controller family is solely responsible. (notebookcheck.net, guru3d.com)

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Final analysis and recommended watchlist for users and admins​

This cluster of reports is a high‑impact, low‑evidence signal: the potential consequences (data corruption or inaccessible partitions) are severe for affected users, but the current public evidence does not establish a global, large‑scale failure affecting all NVMe drives. Pragmatic, conservative steps are therefore appropriate:

• Prioritize backups and avoid high‑volume single writes on recently patched systems with consumer NVMe SSDs.
• Hold off on installing KB5063878 on mission‑critical machines until vendor and Microsoft confirmations appear — or at least stage the rollout behind an image/backup strategy.
• Monitor vendor firmware release notes and Microsoft Release Health for targeted fixes or rollback guidance.
• If you experience a vanished drive mid‑write, image the drive and engage vendor support before attempting destructive repairs.

The technical pattern here is familiar: an OS update alters host behavior in a way that surfaces a firmware edge case. Historically, the effective long‑term remediation has been a combination of vendor firmware patches and narrow host‑side corrections. Until those patches are available, the defensive posture is simple but critical: back up, avoid large writes, stage updates, and follow vendor/Microsoft advisories as they publish verified guidance.

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The evidence to date underscores why disciplined update staging and robust backups remain the first line of defense for everyone who relies on SSDs for important data: when the cost of a single incident is potential data loss, caution is not optional — it is practical system hygiene.

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Source: TechSpot Windows 11 patch linked to SSD data loss, reports remain under investigation