[rudra]

thanks fChk for your appreciation !
I used that dd command cause to me that seemed to be closer to the real / available / usable performance. I agree that it is usually the speed of write to write cache. But that is what we experience in our normal use.

using conv fdatasync asks the os to write from write cache to physical disk before dd exits. so here all the writes are first done to the cache and then purged to the disk. i guess it has a component of write to the disk time. so may be that's why some consider it as the measure of disk performance in a system. but in today's computers of huge cache and parallel access requests, cache purging to the disk time may not be that noticeable in real usage, unless the system is bogged down by write requests to overflow the cache...lol

oflag direct or dsync etc flag is kinda the synchronous access speed ....one may say the real speed of the disk.

i will do what you have requested when i get time and post for you. thanks again !!