It’s hard to associate slowness with an SSD. But over time, your new SSD will slow down, causing longer boot times, poor file transfer speeds, and weak benchmark results. It’s tempting to write this off as the drive wearing out or the usual cost of running Windows for a few years.
While those do play a part, there’s another reason your SSD is slowing down, and it has nothing to do with age. Windows ships with a maintenance job that’s supposed to run on its own and optimize your SSD for the best performance, and on a healthy system, it works. However, it can silently stop running after an update or driver change, and nothing in Windows will tell you it’s been broken, causing degraded SSD performance.
SSDs slow down as they fill up
The cache shrinks when free space runs out
Most consumer SSDs use TLC flash, which stores three bits per cell. But TLC is slow to write to directly, so the controller sets aside a chunk of empty cells and writes to them as if they were SLC (one bit per cell). This SLC cache is what lets your drive hit its advertised peak speeds during short bursts. If you’re curious about the finer details, here’s a good primer on how solid-state drives actually work under the hood.
The catch is that the cache is carved out of free space. When your drive is nearly full, there are fewer empty cells available to act as cache. Large writes quickly overflow what little cache remains and fall back to direct TLC speeds, which can be a fraction of the peak. On some drives, sustained write speed drops from several gigabytes per second to well under half of that once the cache runs out.
Free space also matters for the controller’s background housekeeping. Blocks must be erased before they can be rewritten, and that erase cycle needs room to maneuver. With almost every block in use, the controller struggles to keep a pool of pre-erased blocks ready, which adds latency to every subsequent write.
Partitioning won’t save you here. The controller manages flash layout internally, so making an extra partition or leaving one unmounted doesn’t physically reserve any cache area. Keeping a healthy chunk of free space on the drive is the only thing that reliably helps.
WinSAT tells you how fast your SSD actually is
A built-in benchmark to check your storage drive speed
A good way to tell if your SSD is not working at its best is to run a benchmark test to see if you are still getting the speed it’s rated for. There are many ways to test your SSD speed and performance, but for a quick check, you can use another lesser-known but handy built-in tool called WinSAT.
WinSAT is the command-line engine behind the old Windows Experience Index. Microsoft removed the user-facing score screen years ago, but the tool itself still ships with Windows 10 and 11. To use it, press Win, type cmd, and choose Run as administrator. Then run winsat disk -drive C (replacing C with your SSD’s drive letter).
The test finishes in a few minutes and prints sequential read, sequential write, and random I/O numbers directly in the console. You can compare these against your drive’s rated speeds on the manufacturer’s spec sheet. If the sequential write number is sitting well below what the drive was sold at, that’s your first real hint that something is off.
I like WinSAT because it’s fast, doesn’t need an install, and gives me a number I can act on. It’s not as detailed as CrystalDiskMark, but for a quick sanity check before I start troubleshooting, it’s exactly what I need.
TRIM keeps your SSD fast, and Windows already has it
The maintenance job that quietly goes missing
Traditional hard drives get defragmented. The idea is to shuffle file pieces back next to each other so the read head doesn’t have to jump around. SSDs have no moving parts, so defragmenting them doesn’t help, and the extra writes just wear out the flash. What SSDs need instead is TRIM.
TRIM is a command that tells the SSD controller which blocks no longer hold valid data, so it can pre-erase them and keep a pool of clean blocks ready for new writes. Without TRIM, the drive has to do a slower read-erase-rewrite cycle every time it writes to a used block, and write speeds tank. Windows is supposed to send TRIM commands automatically on a schedule, but that schedule can quietly stop working after a system update or a driver change, and the drive gives you no warning.
To run TRIM manually, open an elevated terminal and type defrag /O C: (again, replace C with your SSD’s letter). The /O switch tells Windows to use the right optimization for the drive type, which means TRIM on an SSD, not a classic defrag. The run can take a few minutes. On a neglected SATA SSD, you can sometimes see a 20-30% write speed recovery afterwards. On a healthy NVMe drive, the change is usually small, which is actually good news: it means background TRIM has been working all along.
To make sure it keeps working, search for Defragment and Optimize Drives in the Start menu and open the tool. Find your SSD in the list and check the Scheduled optimization column. It should say On. If it doesn’t, click Change settings and turn it on. Windows then runs TRIM weekly, which is enough for almost everyone.
- OS
-
Windows
- Minimum CPU Specs
-
1Ghz/2 Cores
Windows 11 is Microsoft’s latest operating system featuring a centered Start menu, Snap Layouts, virtual desktops, enhanced security with TPM 2.0, and deeper integration with Microsoft Teams and AI-powered Copilot.
Keep your expensive purchase feeling fast!
After running defrag /O on my main drive, I saw my sequential write speed climb back to where it should be, and the schedule had silently been off for months. That’s the part that bothers me most: there’s no notification, no warning banner, nothing. The drive just gets slower, and you blame the hardware.
If your SSD feels sluggish, run WinSAT first, then defrag /O, and check the schedule. It takes ten minutes, costs nothing, and often solves the problem without you having to buy a new drive or reinstall Windows. The fix has been built in the whole time. Windows just forgot to tell you about it.
