How does Linux software raid-1 work across disks of dissimilar performance.
Would a raid-1 across ssd and hdd partitions give me a mirror of the ssd contents while not impacting the read speed? I only need good read speed.
Or will it just distribute "reads" round-robin between the drives, giving poor read performance?
(I understand and accept that write performance will be as slow as a hdd.)
From the mdadm-developer-blog I would say - you need at least the 3.2.1 version with that policy-stuff. This sounds as if you can define one member as
spareinstead of using it for active reading/writing. So in your case the harddisk should be the spare.