Messages in this thread |  | | Date | Mon, 26 Nov 2001 16:18:15 -0800 | From | Jonathan Lundell <> | Subject | Re: Journaling pointless with today's hard disks? |
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At 12:49 AM +0100 11/27/01, Martin Eriksson wrote: >I sure think the drives could afford the teeny-weeny cost of a power failure >detection unit, that when a power loss/sway is detected, halts all >operations to the platters except for the writing of the current sector.
That's hard to do. You really need to do the power-fail detection on the AC line, or have some sort of energy storage and a dc-dc converter, which is expensive. If you simply detect a drop in dc power, there simply isn't enough margin to reliably write a block.
Years (many years) back, Diablo had a short-lived model (400, IIRC) that had an interesting twist on this. On a power failure, the spinning disk (this was in the days of 14" platters, so plenty of energy) drove the spindle motor as a generator, providing power to the drive electronics for several seconds before it spun down to below operating speed.
Of course, that was in the days of thousands of dollars for maybe 20MB of storage.... -- /Jonathan Lundell. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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