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    SubjectRe: Journaling pointless with today's hard disks?
    "H. Peter Anvin" wrote:
    >
    > Followup to: <9tumf0$dvr$1@cesium.transmeta.com>
    > By author: "H. Peter Anvin" <hpa@zytor.com>
    > In newsgroup: linux.dev.kernel
    > >
    > > Indeed; having explicit write barriers would be a very useful feature,
    > > but the drives MUST default to strict ordering unless reordering (with
    > > write barriers) have been enabled explicitly by the OS.
    > >
    >
    > On the subject of write barriers... such a setup probably should have
    > a serial number field for each write barrier command, and a "WAIT FOR
    > WRITE BARRIER NUMBER #" command -- which will wait until all writes
    > preceeding the specified write barrier has been committed to stable
    > storage. It might also be worthwhile to have the equivalent
    > nonblocking operation -- QUERY LAST WRITE BARRIER COMMITTED.
    >

    For ext3 at least, all that is needed is a barrier which says
    "don't reorder writes across here". Asynchronous behaviour
    beyond that is OK - the disk is free to queue multiple transactions
    internally as long as the barriers are observed. If the power
    goes out we'll just recover up to and including the last-written
    commit block.

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