Comment by dspillett

For write loads this is expected, even for good drives, at some level. They tend to have some faster storage which takes your writes and the controller later pushes the changes to the main body of the drive. If you write in bulk the main, slower, portion can't keep up so the faster cache fills and your write has to wait and will perform as per the slowest part of the drive. Furthermore: good drives tend to have an amount of even faster DRAM cache too, so you'll see two drop-offs in performance during bulk write operations. For mainly read based loads any proper SSD¹ will outperform a traditional drive, but if your use case involves a lot of writing³ you need to make more careful choices⁵ to get good performance.

I can't say I've ever seen a recent SSD (that isn't otherwise faulty) get slow enough to say it is outperformed by a traditional drive, even just counting the fastest end of the disk, but I've certainly seen them drop to around the same speed during a bulk write.

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[1] unlike this sort of thing: https://www.tomshardware.com/news/low-performance-external-m...

[2] get SLC-only⁴ drives, not QLC-with-SLC-cache or just-QLC, and so forth

[3] bulk data processing tasks such as video editing are where you'll feel this significantly, unless your number-crunching is also bottlenecked at the CPU/GPU

[4] SLC-only is going to be very expensive for large drives, even high-grade enterprise drives tend to be MLC-with SLC-cache. SLC>MLC>TLC>QLC…

[5] this can be quite difficult in the “consumer” market because you'll sometimes find a later revision of the same drive having a completely different memory and/or controller arrangement despite the headline model name/number not changing at all – this is one reason why early reviews can be very misleading