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    SubjectRe: Solaris ZFS on Linux [Was: Re: the " 'official' point of view"expressed by regarding reiser4 inclusion]
    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.
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      Last update: 2006-08-02 01:55    [W:0.027 / U:78.168 seconds]
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