"replace hdd with ssd...?"에 답변As a quick answer, if you already own your iMac, yes you can swap the sluggish HD with a 6.0 Gb/s SSD. It'll be waaaay faster !
"Can I make a fusion drive in my iMac with OSX 10.8.2?"에 답변I can confirm this, i've been using / upgrading (up to 10.9.1) my 21.5 mid 2011 imac without any problem with a fusion drive made from terminal commands, the stock 500Go HD and a vertex 3 SSD. Absolutely nothing to say except it rocks !