Simultaneous Or Sequential write operation-- Does it matter in terms of speed?
With multicore processor, does it make sense to parallelize all the file write operation using multi thread, just to get a boost of speed? Of course, all those write operations are independent.
That depends on the disks and their controller. Do they have TCQ/NCQ? Is it RAID? If so that might make some sense. With one regular SATA disk w/o NCQ, it won't.