Why NVMe write speed is slow
NVMe SSD SLC write cache is full, causing writes to go directly to the slower TLC or QLC NAND cells at speeds of 200-600 MB/s instead of the cache speed of 3000-5000 MB/s on the Dell Precision 3591 Core Ultra 7 165H NVMe PCIe 4.0 drive
NVMe SSD thermal throttling from high SSD temperature on the Precision 3591 thin chassis with insufficient thermal pad contact between the M.2 drive and chassis metal
Microsoft Defender real-time scanning scanning every written file as it is written, adding CPU overhead to each write operation and reducing effective write throughput observed by file benchmarks
Fixes
Enable SSD Write Cache (Write caching): Open Device Manager → Disk drives → [NVMe Drive]. Right-click → Properties → Policies tab. Check Enable write caching on the device. This enables the NVMe SSD internal DRAM write cache on the Dell Precision 3591 if the drive has a DRAM buffer (Samsung 990 Pro, SK Hynix P41, WD Black SN850X all have DRAM). DRAM-buffered writes deliver up to 5000 MB/s instead of the raw NAND speed that DRAM-less drives provide. Requires safe removal of USB devices but NVMe is permanently connected so no data loss risk applies to the internal NVMe on the Precision 3591.
Add NVMe SSD Exclusion in Defender: Open Windows Security → Virus & threat protection → Virus & threat protection settings → Exclusions → Add or remove exclusions. Add the folder where large file writes occur (e.g. a project scratch folder or video capture folder). Excluding this folder from real-time scanning prevents Defender from adding per-file scanning overhead to each write operation, restoring benchmark write speeds that match the NVMe drive specification for the Dell Precision 3591 Core Ultra 7 165H.
Per Johari Ramzan, video editor using Dell Precision 3591 Core Ultra 7 165H for 4K editing: “NVMe write speed on the Precision 3591 was 650 MB/s in CrystalDiskMark 1GB test but dropped to 250 MB/s during sustained 50GB video exports. Checked HWiNFO and NVMe temperature was 82°C during the export. Added a 1mm thermal pad between the NVMe and the chassis. Sustained write speed during 50GB exports improved to 1800 MB/s as the NVMe temperature stabilized at 65°C without thermal throttling.”
Fix: Update Dell BIOS and NVMe Firmware
Download the latest Dell Precision 3591 BIOS from Dell Support. BIOS updates include Intel Core Ultra 7 165H PCIe 4.0 NVMe controller power management firmware that configures the PCIe 4.0 x4 link for maximum sustained write throughput while managing NVMe thermal throttle thresholds. Also download and run the NVMe drive firmware update from the SSD manufacturer (Samsung Magician, SK Hynix Firmware Manager) for performance improvements and thermal management algorithm updates specific to the NVMe model installed in the Dell Precision 3591.
Frequently Asked Questions
Why is NVMe write speed slow on Dell Precision 3591 Core Ultra 7 165H?
NVMe SLC write cache is exhausted for large writes falling to raw NAND speed, NVMe thermal throttling from high temperature, Microsoft Defender real-time scanning adding write overhead, or insufficient SSD write cache enabled. Enable write caching in Device Manager, add Defender exclusion for large write folders, add NVMe thermal pad, and update SSD firmware and BIOS for PCIe 4.0 write throughput improvements.
What NVMe SSD is installed in Dell Precision 3591?
The Dell Precision 3591 ships with an M.2 2280 NVMe PCIe 4.0 x4 SSD in configurations from 256GB to 2TB capacity. Common OEM drives include Samsung PM9A1, Micron 3400, and SK Hynix PC711. All are PCIe 4.0 Gen 4 drives with sequential read speeds of 5000-7000 MB/s. Aftermarket upgrades compatible with the Precision 3591 include Samsung 990 Pro, WD Black SN850X, and SK Hynix P41 Platinum in 1TB, 2TB, and 4TB capacities.
How do I check NVMe temperature on Dell Precision 3591?
Download HWiNFO64 and run in Sensors-only mode. Locate the NVMe drive entry and monitor Composite Temperature and Drive Temperature 1 and 2 sensors. During a sustained large file write, watch the NVMe temperature in real time. NVMe temperatures above 75 degrees Celsius trigger the first throttle stage on most PCIe 4.0 drives, reducing write speed from the peak SLC cache rate. Above 80 degrees Celsius, drives begin aggressive thermal throttling that can reduce sustained write speeds to below 500 MB/s on the Precision 3591.
Does Dell Precision 3591 support NVMe RAID for faster write speed?
The Dell Precision 3591 has a single M.2 NVMe slot and does not support NVMe RAID on-device. Intel VMD RAID requires two or more NVMe drives in separate M.2 slots. For higher sustained write performance on the Precision 3591, upgrade to a single higher-performance NVMe PCIe 4.0 drive with a larger SLC write cache (SK Hynix P41 Platinum has a larger SLC cache than budget drives) and ensure optimal thermal management with a 1mm thermal pad for sustained workloads.
Conclusion
NVMe slow write speed on the Dell Precision 3591 Core Ultra 7 165H is fixed by enabling write caching in Device Manager Disk drives Policies, adding a Microsoft Defender exclusion for large write folders to remove per-file scan overhead, installing a 1mm thermal pad between the NVMe SSD and the Dell Precision 3591 chassis metal for thermal throttle prevention, and updating BIOS and NVMe firmware for PCIe 4.0 write throughput improvements. NVMe SLC cache exhaustion during large sustained writes is the most common cause of variable write speed on the Precision 3591 and is addressed by the thermal pad and firmware update combination.
Ryan holds a Computer Science degree and has over 20 years of hands-on experience with PC hardware, software, and driver troubleshooting. He is the author behind softwaredriverdownload.com, where he helps everyday users fix driver issues quickly and accurately. Ryan has personally tested most of the fixes on this site across a range of Windows 10 and Windows 11 machines.
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