Microsoft's August cumulative for Windows 11 version 24H2 (KB5063878, OS Build 26100.4946) has sparked a new round of alarm in the storage community: multiple reports say the patch is associated with drives disappearing, SMART information becoming unreadable, and — in at least some cases reported by end users and a small number of enthusiasts — file system corruption after sustained write activity. The situation has reopened long‑running wounds from the original 24H2 rollout, which caused BSODs and device failures for certain NVMe SSDs unless firmware or registry workarounds were deployed. The official Microsoft release for KB5063878 addresses several security issues and was published on August 12, 2025, but install failures and follow‑on storage complaints have clouded the update’s rollout. (support.microsoft.com, neowin.net)
Two important caveats govern the near term:
Windows will continue to publish official guidance on KB5063878 via the Windows release health and update history pages; SSD vendors will publish firmware advisories and update tools if vendor firmware is implicated. Watch vendor support bulletins and Microsoft’s release health dashboard for official confirmations. (support.microsoft.com, petri.com)
Conclusion: the current evidence shows that KB5063878 and the broader 24H2 ecosystem have a history of exposing storage firmware edge cases. The new reports of disappearing drives and possible corruption are serious and warrant immediate caution — but some of the more detailed technical claims in the recent coverage are not yet independently verified. Prioritize backups, firmware checks, and staged deployments while waiting for vendor/Microsoft investigations to complete.
Source: Neowin Report: Microsoft's latest Windows 11 24H2 update breaks SSDs/HDDs, may corrupt your data
Background / Overview
What triggered the latest concern
The thread began resurfacing after a report from an independent PC builder/enthusiast in Japan — amplified by social posts — that described drives vanishing from Windows after heavy sustained writes (roughly described as reaching ~50 GB of continuous writes and when controller utilization climbed above ~60%). The reporter stated that affected drives would disappear from Windows and their SMART attributes would become inaccessible, and that a reboot restored visibility temporarily while not fixing the underlying instability. The same write patterns reportedly produced a “high likelihood of file corruption” when symptoms appeared. This particular account was summarized by a technology outlet and shared more widely. (neowin.net)How this ties to earlier 24H2 storage problems
This is not the first time Windows 11 24H2 has run into storage issues. During the 24H2 feature update rollout in October 2024, a widely documented incompatibility between Windows’ new Host Memory Buffer (HMB) allocations and certain Western Digital / SanDisk NVMe drives (notably the SN770 and SN580 families) caused recurring BSODs. That earlier problem was traced to changes in how much system RAM Windows allowed SSDs to use as HMB (Windows increased allocations in 24H2 from the previous default), and vendors ultimately issued firmware updates while Microsoft implemented upgrade blocks for affected models. The pattern from late 2024 — driver/OS behavior exposing firmware faults or limitations on controllers — is highly relevant context for interpreting the current reports. (windowslatest.com, tomshardware.com)What’s known and what’s still uncertain
Known, verified facts
- KB5063878 (Windows 11 24H2 cumulative security update, released August 12, 2025) exists and has had installation issues on enterprise deployment channels (WSUS/SCCM), producing 0x80240069 errors for some administrators. Microsoft documented the release and the associated servicing information. (support.microsoft.com, bleepingcomputer.com)
- The broader class of 24H2 storage problems (BSODs, controller errors, instalarion blocks for devices with outdated SSD firmware) from the October 2024 rollout was real, reproducible by many users, and addressed with firmware updates and registry workarounds; Microsoft also engaged with vendors and applied upgrade blocks for affected models while firmware patches rolled out. The HMB allocation change was the central technical narrative for that earlier wave. (tomshardware.com, pcworld.com)
- Community and support forums (Microsoft Answers, Reddit, vendor and OEM support pages) contain multiple independent reports of drives not being detected, intermittent boot failures, BSODs referencing stornvme or RaidPort errors, and at least a handful of users describing irrecoverable data loss or a need to replace drives after applying 24H2 updates. Those posts indicate the problem is not purely theoretical and has produced concrete consumer impact. (learn.microsoft.com, answers.microsoft.com)
Claims that are plausible but not broadly corroborated
- The specific technical characterization in the recent Japanese report — that a memory leak in Windows’ OS‑buffered cache or a drive cache subsystem malfunction is the root cause, and that Phison‑controller DRAM‑less SSDs fail at lower write volumes than other drives — is currently not well corroborated by independent, widely accepted sources (for example, major storage vendors, Microsoft, or cross‑cutting hardware analysis sites have not published a confirmed Phison‑specific failure mode tied to this August 2025 cumulative). The pattern is plausible — OS buffering and HMB interplay can expose controller firmware bugs — but the Phison/DRAM‑less angle remains an isolated claim at this point. The responsible journalistic stance is to treat those details as unverified until storage vendors or Microsoft publish confirmatory investigation results. (neowin.net)
- Reports that the August cumulative causes complete drive corruption with predictable write volumes are currently based on a relatively small set of anecdotal cases. Community anecdotes can be extremely helpful early warning signals, but they do not yet constitute a confirmed, reproducible systemic failure confirmed by Microsoft, a motherboard/SSD vendor, or independent teardown/forensics teams.
Technical analysis: how Windows, HMB and drivers interact with SSD firmware
Host Memory Buffer (HMB) and why it matters
HMB is part of the NVMe specification that lets DRAM‑less SSDs use a portion of main system RAM as an extended cache. This can dramatically improve performance for low‑cost SSDs without onboard DRAM, but it creates a dependency on OS and driver behavior: the operating system must advertise and allocate memory for the SSD’s use, and the SSD’s firmware must cope with the amount and timing of HMB allocations. If the OS allocates more HMB than the SSD’s firmware expects (or if timing and fragmentation cause unexpected behavior), the SSD’s controller may behave badly — ranging from stalls and timeouts to firmware crashes. That is what investigators determined in the original October 2024 24H2 incidents for several Western Digital / SanDisk drives. (tomshardware.com, pcworld.com)OS write buffering and sustained writes
Modern OSes use layered caching: applications issue writes, those writes often enter an OS page cache (buffered writes), then the storage stack issues those writes to the device. Heavy, sustained high‑throughput write workloads (e.g., tens of gigabytes written rapidly) stress multiple subsystems simultaneously — the storage driver, the PCIe/NVMe controller, the SSD firmware’s write buffers and flash translation layer (FTL), and power/thermal controls. If any of those subsystems has a bug or an unsafe assumption, that workload can surface it. Some community reports of drives disappearing and SMART becoming unreadable after sustained writes are consistent with a controller or firmware crash, or with a transient PCIe link failure exacerbated by driver behavior. However, determining whether the root cause is Windows, the NVMe driver, the SSD controller firmware, or even a board‑level electrical problem requires low‑level logs and vendor cooperation. (neowin.net, support.cyberpowerpc.com)What vendors and Microsoft have done (and what to watch for)
- Microsoft’s August 12, 2025 release page documents KB5063878 and its OS build number, and Microsoft acknowledged WSUS/SCCM install issues that produced 0x80240069 — a problem Microsoft said primarily affects enterprise deployment infrastructure. That particular patch does not list a known storage corruption sweeping issue in the published Known Issues section; Microsoft’s documented known issues are the authoritative baseline to watch. (support.microsoft.com, bleepingcomputer.com)
- In 2024–2025, SSD vendors — notably Western Digital / SanDisk — released firmware updates that resolved many of the reported BSODs caused by HMB misallocations. Microsoft and those vendors coordinated to block upgrades on systems where the old firmware remained installed. That pattern of vendor firmware updates plus Microsoft upgrade blocks is the playbook to expect if new device‑level faults are confirmed. (petri.com, windowslatest.com)
- Some system builders and OEM support centers (including PC vendors’ support documentation) have published guidance — including list of affected models — and recommended firmware updates or temporary registry workarounds in absence of firmware. Those vendor pages are intermediary solutions while a manufacturer investigates. (support.cyberpowerpc.com)
Practical guidance: what Windows users and admins should do now
The highest priority for all users is to protect data. The following steps prioritize safety and minimally invasive remediation.Immediate actions for all users (consumer and pro)
- Back up now. If you have any critical data on a Windows 11 24H2 system, back it up to an external drive, network share, or cloud storage before you install further updates or stress the drive. Image the system (disk image) if possible. A one‑time backup is the single best defense against update‑related data loss.
- Pause updates if you manage devices centrally or if you’re nervous about applying KB5063878 immediately. Use Windows Update’s “Pause updates” or your chosen update management tool to delay installing monthly cumulatives until you can confirm vendor guidance.
- Check device firmware. Open vendor tools such as Western Digital Dashboard, Samsung Magician, or your SSD vendor’s recommended update utility and confirm the SSD firmware version is the latest recommended for 24H2 compatibility. Vendors that issued fixes in the past explicitly warned to back up data before flashing firmware. (tomshardware.com, petri.com)
- If you’re seeing symptoms now (drives missing in Explorer, disk errors in Event Viewer, or storage‑related BSODs):
- Do not immediately run destructive recovery tools. First, power down and check BIOS/UEFI — if the drive disappears at the firmware/UEFI level, that suggests firmware or link failure.
- If the drive is in BIOS, but not Windows, check Device Manager and Disk Management; try reseating the drive (power off, unplug, reseat).
- Collect event logs (Event Viewer) and record error messages (for example, stornvme events or controller error codes).
- If the system is repeatedly failing to boot, consider removing the affected drive and mounting it as a secondary on a known‑good system to image/backup before attempting repair.
Actions for IT admins and advanced users
- Assess exposure. Inventory systems with NVMe / DRAM‑less SSDs or those listed by vendors as historically affected. Prioritize backups and firmware updates for those systems.
- Use vendor firmware and diagnostics before rolling 24H2 to more endpoints. Confirm firmware tool output and update logs before permitting the upgrade.
- Consider a registry mitigation if you have a short‑lived emergency: the community discovered that limiting or disabling HMB allocation via the registry reduces or stops BSOD behavior in many cases. The common advice from multiple outlets was to create or edit the HMBAllocationPolicy DWORD under:
- HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\stornvme\Parameters\Device
- Or under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorPort
Set to 0 to disable HMB, or set to a conservative value (reports indicated that a value of 2 maps to the legacy 64MB policy in some configurations). This is a workaround — not a fix — and will likely reduce SSD performance for affected drives. Always document the registry change, test on non‑production machines, and deploy via group policy only if you fully understand the tradeoffs. (tomshardware.com, petri.com) - Block the upgrade for affected models. Historically Microsoft coordinated upgrade blocks with SSD vendors for 24H2; if vendors publish a list of affected models and recommend a minimum firmware, use Microsoft update management to withhold the feature update until compliance is verified. (windowslatest.com)
When to contact vendor support or pursue recovery
- If an SSD shows physical SMART deterioration (rapid increases in reallocated sectors, uncorrectable sector counts) or if firmware updates and reseating do not restore stability, escalate to the SSD vendor. Provide manufacturer logs and, if possible, a full disk image for forensic analysis. Vendors may accept RMA if firmware corruption or a controller fault is found; however, warranty outcomes can vary by region and model.
Risk assessment: how bad is this, really?
- The incident profile is concerning because storage is a single point of failure for most systems. However, there are qualitative points that reduce the scale of the immediate threat:
- The most severe, reproducible incidents from the 24H2 era involved specific NVMe families (WD/SanDisk) and were largely neutralized by vendor firmware plus Microsoft upgrade blocks. That precedent suggests mitigation channels exist and will be used again if a vendor firmware issue is confirmed. (petri.com, windowslatest.com)
- The most alarming new claims (Phison DRAM‑less controllers failing at lower write volumes, or a systemic Windows OS‑buffered memory leak causing indiscriminate corruption across many vendors) are not yet corroborated by multiple independent technical analyses or vendor advisories. Treat those assertions as potential but unproven. (neowin.net)
- The practical risk right now is moderate for users with susceptible drives and heavy write workloads, and low to moderate for general consumers. For enterprise environments with large fleets and heavy disk usage patterns, the organizational impact of dealing with rollbacks, firmware updates, and potential data restoration is material — especially if a small percentage of drives actually fail and require RMA or replacement.
Recommendations and a short checklist
- Back up critical data immediately.
- Pause non‑essential updates until firmware and vendor guidance are confirmed.
- Check SSD firmware tools for updates and update firmware only after backing up data.
- For devices showing errors: collect logs, test the drive in another machine, and if possible create a forensic image before attempting repairs.
- For IT managers: prioritize inventory, deploy targeted upgrade blocks, and plan for staged upgrades with firmware verification gates.
Final analysis: where responsibility sits and what to expect next
The technical pattern we’re seeing — an OS change exposing firmware or controller edge cases — recurs in modern systems where OS, driver, firmware and hardware vendors must interoperate tightly. Historically, the solution path is clear: vendors publish firmware that tolerates OS behavior or Microsoft adjusts allocation/driver behavior, and upgrade blocks prevent further damage while fixes rollout. That cooperative response happened in 2024 with WD/SanDisk and Microsoft, and the same channel is likely to be used again if vendor investigations confirm a firmware/controller problem tied to KB5063878.Two important caveats govern the near term:
- Community reports (including the Japanese report summarized in the recent coverage) are early warnings. They are essential, but they require vendor and Microsoft verification before being taken as firm technical conclusions. The most explosive technical claims (Phison controller weakness, OS memory leaks causing universal corruption) remain unverified by broad, authoritative analysis. (neowin.net)
- Even if the root cause is vendor firmware, the practical responsibility for protecting data falls on users and administrators now: backups, firmware checks, and temporary mitigations are the immediate lines of defense.
Windows will continue to publish official guidance on KB5063878 via the Windows release health and update history pages; SSD vendors will publish firmware advisories and update tools if vendor firmware is implicated. Watch vendor support bulletins and Microsoft’s release health dashboard for official confirmations. (support.microsoft.com, petri.com)
Conclusion: the current evidence shows that KB5063878 and the broader 24H2 ecosystem have a history of exposing storage firmware edge cases. The new reports of disappearing drives and possible corruption are serious and warrant immediate caution — but some of the more detailed technical claims in the recent coverage are not yet independently verified. Prioritize backups, firmware checks, and staged deployments while waiting for vendor/Microsoft investigations to complete.
Source: Neowin Report: Microsoft's latest Windows 11 24H2 update breaks SSDs/HDDs, may corrupt your data
