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    SubjectRe: [patch] ext2/3: document conditions when reliable operation is possible

    > > +Either whole sector is correctly written or nothing is written during
    > > +powerfail.
    > > +
    > > +       Because RAM tends to fail faster than rest of system during
    > > +       powerfail, special hw killing DMA transfers may be necessary;
    > > +       otherwise, disks may write garbage during powerfail.
    > > +       This may be quite common on generic PC machines.
    > > +
    > > +       Note that atomic write is very hard to guarantee for RAID-4/5/6,
    > > +       because it needs to write both changed data, and parity, to
    > > +       different disks. (But it will only really show up in degraded mode).
    > > +       UPS for RAID array should help.
    > Can someone clarify if this is true in raid-6 with just a single disk
    > failure? I don't see why it would be.
    > And if not can the above text be changed to reflect raid 4/5 with a
    > single disk failure and raid 6 with a double disk failure are the
    > modes that have atomicity problems.

    I don't know enough about raid-6, but... I said "degraded mode" above,
    and you can read it as double failure in raid-6 case ;-). I'll prefer
    to avoid too many details here.

    (cesky, pictures)
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      Last update: 2009-08-24 20:47    [W:0.022 / U:18.272 seconds]
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