Windows 11 24H2 Storage Woes: HMB, BSODs, and 2025 SSD Regression

Microsoft’s Windows 11 24H2 rollout has already spawned two separate storage headaches: an earlier compatibility surge that produced looping Blue Screens of Death (BSODs) on certain Western Digital and SanDisk NVMe drives, and a later August 12, 2025 cumulative patch (KB5063878, OS Build 26100.4946) that independent testers say can make some SSDs — especially drives using certain controller families — disappear during sustained large writes, with a risk of unreadable SMART data and file corruption. (tomshardware.com, support.microsoft.com)

Background​

What landed and why people care​

Windows 11 version 24H2 is Microsoft’s major 2024 feature update and — like many big Windows updates — it introduced changes at multiple layers of the storage stack. For owners of specific DRAM‑less NVMe drives, those changes interacted badly with drive firmware behavior and the Host Memory Buffer (HMB) mechanism, producing severe stability issues in autumn 2024. Months later, a cumulative August 12, 2025 security/quality rollup (KB5063878) has been linked by community testing to a different failure pattern: drives that become unresponsive and vanish from the OS during heavy sequential write workloads. (tomshardware.com, guru3d.com)

The Host Memory Buffer (HMB) — short explainer​

HMB lets DRAM‑less NVMe SSDs borrow a small slice of system RAM for caching metadata and mapping tables. It’s a trade-off: sacrificing a tiny amount of system RAM in exchange for better SSD performance without the cost of onboard DRAM. Historically Windows assigned relatively small HMB windows (commonly ~64 MB) to these drives; the 24H2 rollout altered that behavior in some cases and triggered firmware edge conditions on certain drives. Multiple independent outlets and vendor advisories have now documented the interplay between HMB allocation, firmware expectations, and resulting system instability. (techspot.com, neowin.net)

---

Timeline and what happened, step by step​

October 2024 — the HMB/BSOD episode​

Shortly after the initial broad rollout of Windows 11 24H2, users began reporting pervasive BSOD loops on systems equipped with specific WD and SanDisk NVMe models (most frequently: WD Black SN770, WD Blue SN580 and related 2 TB variants, and SanDisk Extreme M.2 in some cases). The crashes commonly reported the “Critical Process Has Died” error or showed storage controller errors in Event Viewer. Community troubleshooting rapidly pointed to HMB allocation changes as a likely trigger. (tomshardware.com, answers.microsoft.com)
Manufacturers reacted: Western Digital and SanDisk released firmware updates for affected models and their support pages and tools (Western Digital Dashboard / SanDisk Dashboard) were updated to deliver the fixes and guidance. Microsoft also implemented upgrade blocks for systems with out‑of‑date firmware to prevent further automatic distribution of the 24H2 feature update to vulnerable hardware. That combination (firmware from vendors + Microsoft’s rollout controls) is the primary remediation path Microsoft and vendors recommended. (support-en.sandisk.com, tomshardware.com)

Registry workarounds and user fixes​

Before vendor firmware was widely applied, community developers and some OEMs published registry workarounds that limited or disabled HMB on affected systems. The commonly discussed registry key was HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorPort\HmbAllocationPolicy, with numeric values used to disable HMB or restrict its allocation. This approach provided a pragmatic stopgap for many users but came with clear trade‑offs: reduced SSD performance and the usual risks of editing the Windows Registry. Multiple outlets reproduced the registry tweak and described it as a practical but temporary fix while vendors issued firmware. (tomshardware.com, neowin.net)

August 12, 2025 — KB5063878 and a new pattern​

On August 12, 2025 Microsoft released cumulative update KB5063878 (OS Build 26100.4946) for Windows 11 24H2. The official KB page initially listed no known issues. Within days, however, independent testers and multiple enthusiast outlets began reproducing a separate regression: during sustained, large sequential writes (community repros often cited transfer volumes of ~50 GB or higher), some NVMe SSDs — particularly drives with certain Phison controllers and DRAM‑less designs — can stop responding, disappear from Device Manager and Disk Management, and become unreadable to SMART or vendor diagnostic utilities. In a subset of reports, files written during the failure window were corrupted or went missing. Reboots sometimes restored drive visibility but did not guarantee integrity of the affected writes. (support.microsoft.com, guru3d.com, tomshardware.com)

---

Technical analysis: why two different but related failures occurred​

Shared surface: OS storage stack changes​

Both incidents trace back to the same broad principle: a subtle change in how Windows interacts with SSDs can expose latent controller/firmware bugs. The OS, storage drivers (stornvme, StorPort, VMD, etc.) and the SSD controller firmware cooperate tightly; changes in command timing, buffer sizes, DMA behavior or HMB allocation can move a controller from nominal to an edge condition it wasn’t designed to handle. When that happens, symptoms range from kernel crashes (BSOD) to controller hangs that make the drive disappear from the PCIe/NVMe topology. Community engineering analyses that reproduce failures often point at timing or buffer allocation regressions in host-side behavior as plausible root causes. (guru3d.com)

HMB allocation specifics — what the reporting shows (and what remains unverified)​

Multiple community reproductions and tech outlets reported that affected drives were requesting or being assigned up to ~200 MB of HMB after 24H2 — substantially higher than the ~64 MB allocations observed previously — and that older firmware on some 2 TB models could not handle the larger window. That mismatch appears to be the proximate cause of the October 2024 BSODs on some WD/SanDisk models. Independent testing and vendor advisories corroborated that firmware updates resolved the BSOD pattern in the majority of cases. That said, the exact negotiation steps and whether every reproduction used precisely 200 MB varies across reports, and no single Microsoft engineering bulletin enumerated those low‑level HMB bytes publicly at first — so treat the 200 MB figure as a widely reported, community‑verified value rather than a Microsoft‑published constant. (techspot.com, neowin.net)

The August 2025 KB incident — sustained write workload exposes another edge​

The KB5063878 pattern differs: it reproduces with large continuous write loads, and the devices involved extend beyond a single brand or model. Many affected devices used Phison controller families or DRAM‑less designs, but community lists vary and are not exhaustive. The KR here is that heavy, sustained writes stress internal SSD metadata and mapping operations; a host-side timing or buffering regression (introduced in the cumulative update) apparently causes the SSD controller to stall or crash. When that happens, the OS may report the device as gone and vendor utilities may no longer read SMART or controller telemetry. That pattern increases the risk of file corruption for in-flight data. (guru3d.com, tomshardware.com)

---

What vendors and Microsoft have done so far​

• Western Digital / SanDisk: issued targeted firmware updates for affected models and published support pages and dashboard tools to deliver firmware. Their advisories explicitly warn users to back up critical data before applying firmware and note Microsoft may block upgrades until firmware is updated. (support-en.sandisk.com, tomshardware.com)
• Microsoft: used upgrade blocks during the initial 24H2 feature rollout to prevent systems with known‑vulnerable firmware from being offered the update automatically, and released cumulative updates via Windows Update. For KB5063878, Microsoft’s public KB page initially listed no known issues even as community reports surfaced; Microsoft’s update‑health mechanisms (release‑health and blockings) were later used to mitigate enterprise deployment regressions where applicable. The discrepancy between the KB page and community evidence has been a focal point for criticism. (windowslatest.com, support.microsoft.com)
• Community/enthusiast testers: reproduced failures, published reproducible write profiles, and assembled lists of suspect models and controller families. Their work drove vendor firmware patches and prompted administrators to apply cautious rollout policies.

---

Practical guidance for users and administrators​

The single most important theme here is risk management: protect your data, update firmware and drivers carefully, and avoid risky write workloads until your system and SSD firmware are confirmed good.

For home users — immediate checklist​

• Back up critical data now. Use an external drive or cloud backup before you change firmware, install updates, or perform big transfers.
• Check your Windows build: Settings → System → About → OS build. If you have KB5063878 (OS Build 26100.4946) installed and you rely on heavy writes, postpone large file transfers until vendors confirm compatibility.
• Identify your SSD model:
• Device Manager → Disk drives, or use vendor tools (WD Dashboard, SanDisk Dashboard) to display model and firmware.
• Update SSD firmware if your drive is on vendor lists:
• Use Western Digital Dashboard or SanDisk Dashboard to check for and apply firmware updates. Follow vendor instructions precisely and back up first; firmware updates sometimes require a power cycle and can carry a small but real risk of data loss. (support-en.sandisk.com, tomshardware.com)
• If you’re experiencing BSOD loops after 24H2 and a firmware update isn’t available, consider the registry mitigation:
• Edit HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\StorPort\HmbAllocationPolicy. Values discussed in community threads included 0 (disable HMB) or values intended to restrict allocation size. Use this only as a last resort, and back up the Registry before changes. Be aware: disabling HMB may reduce SSD performance. (neowin.net, tomshardware.com)

If a drive disappears mid‑transfer (recommendation)​

• Stop further write activity immediately. Don’t retry the same transfer repeatedly.
• Note whether the drive shows in Device Manager or Disk Management. If it’s missing, try a graceful reboot. Rebooting has restored visibility for many users, but it does not guarantee data integrity for interrupted writes.
• Use vendor tools (WD/SanDisk Dashboard, CrystalDiskInfo, vendor utilities) to query SMART and firmware. If telemetry is unreadable, assume potential corruption.
• Restore from backup if essential files are missing. If you lack backups, image the affected disk (sector‑by‑sector) before further action and consult professional recovery tools or services; attempting random writes can make recovery harder.
• For enterprise fleets, roll back the problematic cumulative update in controlled environments using WSUS/SCCM or the appropriate update management path; monitor vendor advisories and Microsoft release health before mass redeployment. (tomshardware.com, guru3d.com)

For administrators — specific flags​

• Monitor WSUS/SCCM deployment errors; the August 2025 package produced known enterprise installation regressions (0x80240069) for some admins and warranted re-releases or Known Issue Rollback (KIR) mitigations in other cases. Hold non‑urgent deployments until compatibility is confirmed. (guru3d.com)

---

Strengths and weaknesses in the response ecosystem​

What went right​

• Vendor responsiveness: Western Digital and SanDisk produced firmware updates and dashboard tooling to address the HMB/BSOD pattern, and many affected users report recovery after applying vendor firmware. That the vendors identified firmware fixes indicates the problem’s root plausibility and that remediation is feasible. (tomshardware.com, support-en.sandisk.com)
• Community engineering: enthusiasts and sysadmins reproduced issues, published triggers and mitigations, and accelerated vendor and Microsoft attention. Community telemetry remains valuable in cases that escape initial QA.

What went poorly — and why it matters​

• Timing and communication gaps: Microsoft’s KB entry for KB5063878 initially listed no known issues while community testing already flagged a storage regression; inconsistent public messaging increases exposure risk for users performing heavy write workloads. That mismatch between published KB information and community experience is a serious operational failing. (support.microsoft.com, tomshardware.com)
• Test coverage and regression risk: modern SSD firmware, HMB negotiation, and host drivers produce a multidimensional compatibility matrix. The incidents show that even well‑tested OS releases can expose controller firmware edge cases. The pace of feature rollouts and the reliance on staging via Insider and staged distribution may reduce the margin for catching every hardware-specific regression.
• Data risk: the KB5063878 failure mode is not just an inconvenience; it can corrupt or make in‑flight data unrecoverable. That elevates the issue from a stability annoyance to a data‑integrity emergency for users who routinely perform large writes.

---

Risk assessment: how worried should you be?​

• If you have a modern NVMe drive from a mainstream vendor (Samsung, Western Digital, SanDisk, Corsair, etc.), the probability of encountering an issue depends on model, firmware revision, and workload profile. The initial 24H2 BSOD narrative showed a strong concentration on specific WD/SanDisk 2 TB models with older firmware; the later KB regression affects a broader set but remains, according to community evidence, non‑universal. (tomshardware.com, guru3d.com)
• The impact for affected cases can be high: repeated BSODs, system instability, drive invisibility, and potential file corruption/loss for large writes that fail mid‑stream. Therefore, the conservative posture for users who handle critical data is to back up aggressively and delay updates until vendor compatibility is confirmed.

---

Recommendations — durable, practical steps​

• Backup discipline: ensure you have an up‑to‑date, verifiable backup (both local and off‑site/cloud) before applying major OS or firmware updates.
• Firmware first, update second: check vendor dashboards for firmware updates before accepting the 24H2 feature upgrade or recent cumulative updates. Vendors may publish critical firmware that Microsoft’s update blocks rely on to allow safe upgrades. (support-en.sandisk.com, tomshardware.com)
• Avoid large, sustained sequential writes on systems that recently installed KB5063878 until vendors confirm fixes or Microsoft updates the KB with a known‑issue entry and mitigation steps. If you must perform big writes, use an alternative, unaffected drive or perform the transfer on a system that is confirmed compatible. (tomshardware.com, guru3d.com)
• Enterprise caution: hold or stage the August 12, 2025 update in test rings, validate with your workload profiles (especially backups, imaging, AV scans, and installer packages) and monitor for deployment error 0x80240069 and storage regressions. Plan rollback playbooks that include restoring files from backup, not just OS patches. (guru3d.com)
• If you rely on registry mitigations, document them and understand performance trade‑offs. Prefer vendor firmware patches whenever available. (neowin.net)

---

Final assessment and takeaways​

The Windows 11 24H2 episode and the subsequent August 2025 cumulative update illustrate how fragile the interaction between OS storage stacks and SSD controller firmware can be. In this case, two distinct failures emerged from similar root causes: small changes in host behaviour (HMB allocation and buffer/timing changes) pushing controllers into previously unobserved edge conditions. Vendor firmware updates have addressed many 24H2 BSOD cases, underscoring that controller firmware responsibility is real and remediable. At the same time, the later cumulative update demonstrates the ongoing risk that routine security/quality patches carry for devices under heavy I/O.
The practical advice is straightforward: prioritize backups, apply vendor firmware before major OS upgrades, stage updates for enterprise environments, and avoid high‑volume write workloads until compatibility is confirmed. The community’s rapid reproduction and vendor fixes are positive signs, but the incidents also reveal a pressing need for clearer vendor/Microsoft communication and more exhaustive real‑world workload testing before broad deployment.
For Windows users who prize system stability and data integrity, the safest posture for the immediate term is conservative: verify firmware and backups, defer high‑risk operations, and watch vendor advisories and Microsoft’s release‑health pages for confirmed fixes or known‑issue disclosures. (tomshardware.com, support-en.sandisk.com, support.microsoft.com)

---

Conclusion
Software and hardware both change constantly; when they do, thin margins turn into system‑wide failures. The Windows 11 24H2 saga is a reminder that updates — no matter how well intentioned — must be approached with caution when they touch storage. Prioritize backups, keep firmware current, and treat large updates like critical projects: test, stage, verify, and only then roll them into production.

---

Source: TechPowerUp Microsoft Windows 11 24H2 Update May Cause SSD Failures