Question: I was examining a new hard drive when I noticed something peculiar:

It’s a 1 TB HDD from Seagate, and CrystalDiskInfo shows that it supports TRIM! AFAIK, TRIM is some SSD feature that allows the controller to recycle and erased unused pages for better write performance in the future. But HDD just overwrites the old data and doesn’t need any “deletion notify”.

What does this TRIM support on an HDD indicate?

Answer: This probably means that your HDD is an SMR drive. Since SMR drives work differently, a TRIM operation is needed to improve performance over time.

WD’s support page provides a good explanation for this:

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TRIM/UNMAP is supported for external hard drives with SMR (Shingled Magnetic Recording) drive inside, like SSDs, for dataset management and to improve SMR performance over time. One of the shingled write benefits is that all physical sectors are written sequentially in a direction radially and are only rewritten after a wrap-around. Rewriting a previously written LBA (Logical Block Addressing) will cause the previous write to be marked invalid and the LBA will be written to the next sequential physical sector. The TRIM/UNMAP enables the OS to inform the drive which blocks are no longer considered to be in use and can be reclaimed internally by the HDD to ensure that later write operations perform at full speed.