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TRIM
In brief
TRIM is a command with which the operating system tells an SSD which data blocks are no longer needed, for example after a file is deleted. The SSD can then release these blocks in the background and thus stays fast and wears evenly. However, TRIM is not an erasure method for IT retirement, because it guarantees neither complete nor verifiable erasure.
How does SSD TRIM work?
Flash memory cannot simply overwrite data. A block must first be erased before it can be written to again. Without TRIM, the SSD does not know which data the file system already considers deleted and keeps carrying it along. With TRIM, the operating system marks these areas. The internal garbage collection can then consolidate and erase them. This improves write performance and supports Wear leveling.
Depending on the interface, the command has different names: TRIM for SATA, Deallocate for NVMe and UNMAP for SCSI and SAS. Modern operating systems send it automatically.
Why TRIM does not replace secure erasure
- When the SSD actually erases the marked blocks is decided by the controller. There is no guarantee.
- Reserve areas and retired blocks are not reliably captured.
- No report is generated that proves erasure for each data carrier.
Even a Quick format often triggers TRIM for the entire data carrier on SSDs. This makes data invisible to simple tools but is not a verified erasure method. Which methods are suitable for SSDs is shown in the guide Securely erasing hard drives and SSDs. Second IT erases SSDs with Blancco and issues a digitally signed erasure certificate for each device.
Frequently asked questions about TRIM
Should TRIM be enabled on an SSD?
Yes, TRIM makes sense during normal operation. Modern operating systems usually enable it automatically for SSDs.
Is data permanently gone after TRIM?
Often they can no longer be read with simple means. There is no guarantee, however, and reserve areas are not taken into account. TRIM is therefore not sufficient for retirement.
Does TRIM also exist for hard drives?
Classic magnetic hard drives do not need TRIM. Exceptions are hard drives with certain recording methods that use similar commands.
What is the difference between TRIM, Deallocate and UNMAP?
It is the same function with different names depending on the interface. The command is called TRIM for SATA, Deallocate for NVMe and UNMAP for SCSI and SAS. The operating system uses it to tell the SSD which blocks are no longer needed. Modern operating systems send it automatically.
Is a quick format on SSDs a secure erasure?
No. A quick format often triggers TRIM for the entire data carrier on SSDs. This makes data invisible to simple tools but is not a verified erasure method. No report is generated that proves erasure for each data carrier.
Verifiably erase SSDs instead of just trimming them.
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