Is TRIM working on your external SSD? How to check on a Mac, and when it matters
Apple's own SSDs always use TRIM. External SSDs depend on the connection and the drive. How to check, what trimforce does, and when to worry.
TRIM lets macOS tell an SSD which blocks are no longer in use, so the drive can prepare them for new writes. Without it, an SSD can slow down over time as it fills and empties. Your Mac's internal SSD always has it. External drives vary.
Check whether a drive has TRIM
Open System Information, then look under Hardware at NVMExpress, SATA or USB, depending on how the drive connects. Select the drive and look for TRIM Support.
system_profiler SPNVMeDataType SPSerialATADataType 2>/dev/null | grep -Ei "model|trim"What to expect
| Drive | TRIM on a Mac |
|---|---|
| Apple internal SSD | Always on |
| NVMe SSD over Thunderbolt or USB4 | Usually works |
| Third-party SATA SSD installed inside an older Mac | Off until you enable it |
| SSD in a USB enclosure | Often not passed through by macOS |
trimforce
For third-party SATA SSDs, macOS can turn TRIM on with one command. It asks you to confirm and restarts the Mac:
sudo trimforce enableIt does not add TRIM to USB enclosures.
Does it matter?
For an archive drive written once and read later, hardly at all. For a drive you fill and empty constantly, such as a video scratch disk, a drive with TRIM, or one connected over Thunderbolt, keeps speeds steadier. Leaving some free space on the drive also helps.
Choosing a drive: external SSD or hard drive. Its health: SSD lifespan and a full disk.
Common questions
Does macOS support TRIM on external SSDs?
Usually for NVMe drives over Thunderbolt or USB4. SSDs in USB enclosures often do not receive TRIM on a Mac.
What does trimforce do?
It turns on TRIM for third-party SATA SSDs. It does not affect USB drives.
How do I check if TRIM is enabled on my Mac?
Open System Information, find the drive under NVMExpress, SATA or USB, and look for TRIM Support.