On 4/24/2018 5:37 AM, Michael Kjörling wrote:
>
> I couldn't quite resist, so tried it out. Take this for what it is, an
> anecdote.
>
To make it even worse in terms of trying to figure out what a disk will 
do for (to) you in terms of performance...

A new caching scheme on a set of 10TB drives I bought a while ago - they 
are HGST SAS drives.

They incorporated a set of cylinders spaced across the disk that are 
"cache" cylinders. Wherever the heads are "right now", the closest cache 
cylinders will be used to write to. Once there's enough free time, it 
will go back and read those cache cylinders, and put the blocks where 
they are "supposed" to be.

http://www.tomsitpro.com/articles/hgst-ultrastar-c15k600-hdd,2-906-3.html

Those are not the drives I bought, but as far as I know, even their 
near-line SAS products have this feature, called NVC Quick Cache

ak