For the second part of your question, the answer is "yes". All RAID functions specify using identical drives. Striping different size drives lowers the performance to the lowest common denominator. Larger drives will have a higher average seek time (assuming same rotational speed.) Although what you suggest is doable, most will not recommend it or support it.
And, for the final part of your question, response performance of the first drive will be negatively affected by the lower speed second drive. Again it's doable, but most will not recommend or support this. You are opening yourself up to errors as well. You are better off using asynchronous mirroring between arrays where the second array has lower cost and speed drives.
Dig Deeper on RAID
Related Q&A from Marc Staimer
There are three ways to implement hybrid cloud storage, and the biggest difference between them comes down to management.continue reading
Marc Staimer of Dragon Slayer Consulting explains what causes read disturbs and how flash vendors are mitigating the issue.continue reading
Marc Staimer of Dragon Slayer Consulting compares NVDIMM and memory channel flash, explaining the advantages and disadvantages of each.continue reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.