Is your SSD slower than it should be? How to check and fix it

What speed to expect

Drive	Typical sequential read
SATA SSD	500–560 MB/s
NVMe SSD, PCIe 3.0	1,500–3,500 MB/s
NVMe SSD, PCIe 4.0	3,500–7,400 MB/s
NVMe SSD, PCIe 5.0	10,000 to about 15,000 MB/s
Mechanical hard drive	100–250 MB/s

Your own drive’s figure is on its maker’s website. For everyday speed, small random reads matter more than these headline figures, and every SSD is far ahead of a hard drive at those.

To measure yours, run a disk benchmark such as the free CrystalDiskMark with nothing else running, and compare its first result, the sequential read, with the maker’s figure. Well under it is worth looking into.

1. It is nearly full

An SSD needs empty space to work quickly: as it fills, writing slows down, and many slow down sharply in the last 10–15%. Keep at least 15–20% free. Settings → System → Storage shows what is taking the space, and Storage Sense on the same page can clear temporary files and the recycle bin automatically.

2. TRIM is switched off

When you delete a file, Windows normally tells the SSD straight away, with a command called TRIM, so that the drive can clear the space in advance. With TRIM off, the drive finds out only when the space is written again and has to clear it then, so writing gets slower over time. TRIM is on by default; some old tuning tools switch it off.

1. Right-click the Start button and choose Terminal (Admin) (on Windows 10, Windows PowerShell (Admin)).
2. Type fsutil behavior query DisableDeleteNotify and press Enter.
3. The setting is called DisableDeleteNotify, so it reads backwards: NTFS DisableDeleteNotify = 0 means TRIM is on, and 1 means it is off.
4. To switch it on, type fsutil behavior set DisableDeleteNotify 0 and press Enter.

Then open Defragment and Optimize Drives from Start, select the SSD and choose Optimize. On an SSD this does not defragment anything: it sends TRIM for all the free space at once, catching up on what was missed. The same window shows that Windows does this by itself on a schedule, usually weekly.

3. An NVMe drive in a slow slot

An NVMe drive reaches its speed only in a slot with enough PCIe lanes of a recent enough generation. A PCIe 4.0 drive that never reads faster than about 3,500 MB/s is in a slot with half the bandwidth it needs; an NVMe drive reading around 500 MB/s, the speed of a SATA drive, is badly held back.

• The motherboard’s manual has a table of its M.2 slots: which connect straight to the processor (normally the fastest, nearest to it), which go through the chipset, and which share their lanes with SATA ports or a second graphics slot — using one can slow another.
• Move the drive to the processor-connected slot if it is in another.
• In the firmware, check that the slot is not set to an older PCIe generation.
• A drive in a USB enclosure or adapter runs at the speed of the USB connection, however fast the drive.

4. Fast at first, then slow during long copies

Many SSDs write into a fast cache and slow down once it is full, during a copy of tens of gigabytes. Models without their own memory chip (DRAM-less) and QLC drives can drop below a hard drive’s speed for the rest of the copy. That is how they are designed, not a fault, and it only matters if you often copy large amounts at once.

5. Heat

NVMe drives slow themselves down when they get hot, often from around 70–80 °C. A drive under a graphics card without a heatsink can reach that during long transfers or while a game loads. Most recent motherboards come with a heatsink for the main M.2 slot, and fitting it is usually enough.

6. Firmware

Drive makers fix performance problems in firmware updates. Samsung Magician, WD Dashboard, Crucial Storage Executive and Kingston SSD Manager check for them and install them; back up first. Windows’ own NVMe driver is right for almost every drive.

7. Wear

A very worn or failing SSD slows down as it retries reads. How to check drive health.

What not to do

Do not run a third-party defragmenter on an SSD: it wears the drive and gains nothing. Windows’ Defragment and Optimize Drives already does the right thing for each kind of drive.

How Bottleneck checks this

A scan measures every drive’s read, write and random-read speed and compares it with what that kind of drive should manage. It reports an NVMe drive running at SATA speeds, with how to find the right slot, as well as TRIM switched off, drives that are nearly full, too hot, worn or failing, and Windows on a hard drive.