James G. Sack (jim) wrote:
I think this has been asked elsewhere, and probably more than once, but I wonder why drives cannot save the cache during the power-down ramp.
The power requirements are too high. In order to do it, especially with the high capacity caches that drives have, the drive would have to be kept spinning within and acceptable RPM range for a minimum number of milliseconds. Add the power draw of the other electronics, and in order to do it the drive would need some power storage (capacitor bank) in order to accomplish it. It would also need circuitry to detect the drop in supply voltage/current, and some circuitry to stop any current reads and initiate the write immediately.
Sure, it could be done, but it would increase the price of the drive and mfgs. don't want to do that. QUAKE did not want to do that with the embedded systems despite requests from customers. In their case, it was only a matter of putting a single high capacity capacitor (heh, reading that sounds funny) on the board increasing the cost by about $5 per unit (not including a board spin, testing the new boards, etc. which would be NRE - Non-Recoverable Engineering costs). The units already have circuitry and software to detect low power conditions.
I guess hybrid drives are another solution to this problem, eh.
Possibly, but that depends upon the design (see above). PGA -- Paul G. Allen, BSIT/SE Owner, Sr. Engineer Random Logic Consulting http://www.randomlogic.com -- [email protected] http://www.kernel-panic.org/cgi-bin/mailman/listinfo/kplug-list
