Messages in this thread | | | Date | Wed, 02 Aug 2006 00:50:49 +0100 | From | Ian Stirling <> | Subject | Re: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressed by kernelnewbies.org regarding reiser4 inclusion] |
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David Masover wrote: > David Lang wrote: > >> On Mon, 31 Jul 2006, David Masover wrote: >> >>> Oh, I'm curious -- do hard drives ever carry enough >>> battery/capacitance to cover their caches? It doesn't seem like it >>> would be that hard/expensive, and if it is done that way, then I >>> think it's valid to leave them on. You could just say that other >>> filesystems aren't taking as much advantage of newer drive features >>> as Reiser :P >> >> >> there are no drives that have the ability to flush their cache after >> they loose power. > > > Aha, so back to the usual argument: UPS! It takes a fraction of a > second to flush that cache.
You probably don't actually want to flush the cache - but to write to a journal. 16M of cache - split into 32000 writes to single sectors spread over the disk could well take several minutes to write. Slapping it onto a journal would take well under .2 seconds. That's a non-trivial amount of storage though - 3J or so, 40mF@12V - a moderately large/expensive capacitor.
And if you've got to spin the drive up, you've just added another order of magnitude.
You can see why a flash backup of the write cache may be nicer. You can do it if the disk isn't spinning. It uses moderately less energy - and at a much lower rate, which means the power supply can be _much_ cheaper. I'd guess it's the difference between under $2 and $10. And if you can use it as a lazy write cache for laptops - things just got better battery life wise too. - 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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