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    SubjectRe: lack of raw disk devices
    > Okay. I've seen this dicussion many times before. I need to know now. What the
    > hell is the difference a RAW block device and a (err.... NONRAW?) regular block
    > device?

    A raw device doesn't go through the buffer cache. For example, if you
    issue two reads for the same block, a raw device will physically go
    out to disk each time, whereas a buffered device will satisfy the
    second request from the cache.

    I've read all of the discussion I can find about this, in linux-kernel
    archives and elsewhere, and while I don't want to beat a dead horse, I
    disagree with those who say raw devices are useless or intrinsically
    bad. Granted, the vast majority of the time a buffered device is the
    right thing. But I have one application in mind that cries out for a
    raw device---it involves moving digital video as fast as possible from
    disk to DRAM (and subsequently out to a PCI bus master). The system
    will never again need to refer to this data, so a buffered device both
    incurs a copying expense (from buffer cache to DRAM buffer) and
    trashes the buffer cache to no purpose.

    Cheers,
    Peter Monta pmonta@imedia.com
    Imedia Corp.

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