There is whats called a cache and a queue, every hard drive has a flash chip for storing stuff that arrives from sata. And until the head is ready to write, information stays in that cache. There is also a queue, so the more files or stuff you got going in, the longer it is, so the slower everything works.
Would putting 2 ssd's in RAID 0 be cheaper then a SAS drive ? (rufee's not sure how much sas'es go for)
We are so going off topic here anyway, why do you think core routers cost millions of dollars?