~20 years ago I was helping someone with their storage server for their mail server, it had 8x 10K discs in a RAID-1. It was always struggling to keep up and often couldn't keep up. Intel had just come out with their SSDs, and I had a friend with access to one that was larger in size than the array. I shipped this little laptop drive off to get installed in the storage server.
Once the SSD was on the server, I did a "pvmove" to move the data from spinning array to SSD, while the system was up and running. Over the next several hours the load on the server dropped. It was comical that these 8 hard drives could be replaced by something smaller than my wallet.
If those drives were short-stroked, they probably could have kept up with that SSD, though at a reduced capacity. SSD would probably have a lower power bill over its life, though. I did some calculations for an array of short-stroked 15k SAS disks to replace a consumer 4GB SSD for a write-intensive app that chews through SSDs, and its performance would be in spitting distance of the SSD. Ended up not doing it due to likely not having any parts availability for 15k SAS drives in the not too distant future.
Except that we would have needed a lot more than the 8 drives then, to keep the same capacity. I think it was 1TB of storage around 1999. For mail storage it unfortunately needed both capacity and seek latency.
Once the SSD was on the server, I did a "pvmove" to move the data from spinning array to SSD, while the system was up and running. Over the next several hours the load on the server dropped. It was comical that these 8 hard drives could be replaced by something smaller than my wallet.
But pvmove was the other star of this show.