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The general rule I use is to look at the DRAM size, if it is:

* 256 MB (or more) - most likely it’s an SMR drive

* 64-128 MB almost guaranteed it’s an PMR drive

I base this on my observation, that I’ve never seen an SMR drive with less than 256 MB of cache.

It really depends, newer Toshiba and HGST drives in "massive" (ie > 8TB) sizes are almost all 256MB cache for improved in-memory write reordering, but HGST calls out at least some of their drives as not only being PMR but also being better because they're PMR [0] (it's just the most recent one we purchased for our ZFS pool). We haven't had any issues with it (first order of business is writing random values to the disk then reading them back to verify integrity and check SMART values afterwards) and had sustained write speeds the entire time.

"Designed to handle workloads up to 550TB per year, the Ultrastar DC HC520 is the industry’s first 12TB drive and uses traditional perpendicular magnetic recording (PMR) technology to make it dropin ready for any enterprise-capacity application or environment."

[0]: https://documents.westerndigital.com/content/dam/doc-library... (search PMR)

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