[epistasis]

I would say that Ceph+RadosGW works well with HDDs, as long as 1) you use SDDs for the index pool, and 2) you are realistic about the number of IOPs you can get out of your pool of HDDs.

And remember that there's a multiplication of iops for any individual client iop, whether you're using triplicate storare or erasure coding. S3 also has iop multiplication, which they solve with tons of HDDs.

For big object storage that's mostly streaming 4MB chunks, this is no big deal. If you have tons of small random reads and writes across many keys or a single big key, that's when you need to make sure your backing store can keep up.