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    SubjectRe: ATA 4 KiB sector issues.
    >>>>> "Cláudio" == Cláudio Martins <> writes:

    Cláudio> So the question is: what are hard drive makers guaranteeing (if
    Cláudio> anything at all)?

    No guarantees. Nothing that you can get in writing, anyway.

    Cláudio> Was a 512B sector write really atomic?


    Cláudio> Is a 4k one?

    Sometimes, maybe.

    The problem with 4KB physical blocks is that if you do a partial or
    misaligned write you'll end up having to do read-modify-write. And that
    introduces are scenario where a subsequent write error will affect
    logical blocks that were not part of the I/O request.

    However, you also have that with regular drives because they often write
    more than the actual block undergoing I/O. For instance to reduce
    hotspot bleed to adjacent sectors.

    There have been several unsuccessful attempts at nudging the drive
    vendors into giving us real guarantees (supercapacitors, NVRAM or
    flash-backed write cache). No luck so far. So people that care use
    arrays with non-volatile caches.

    Martin K. Petersen Oracle Linux Engineering
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      Last update: 2010-03-08 22:11    [W:0.020 / U:10.100 seconds]
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