# [OmniOS-discuss] 4kn or 512e with ashift=12

Bob Friesenhahn bfriesen at simple.dallas.tx.us
Thu Mar 24 01:37:19 UTC 2016

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    On Wed, 23 Mar 2016, Richard Elling wrote:

    >
    >> On Mar 23, 2016, at 7:49 AM, Richard Jahnel <rjahnel at ellipseinc.com> wrote:
    >>
    >> It should be noted that using a 512e disk as a 512n disk subjects you to a significant risk of silent corruption in the event of power loss. Because 512e disks does a read>modify>write operation to modify 512byte chunk of a 4k sector, zfs won't know about the other 7 corrupted 512e sectors in the event of a power loss during a write operation. So when discards the incomplete txg on reboot, it won't do anything about the other 7 512e sectors it doesn't know were affected.
    >
    > Disagree. The risk is no greater than HDDs today with their volatile write caches.

    If the data unrelated to the current transaction group is read and
    then partially modifed (possibly with data corruption due to loss of
    power during write), this would seem to be worse than loss due to a
    volatile write cache (assuming drives which observe cache sync
    requests) since data unrelated to the current transaction group may
    have been modified.  The end result would be checksum errors during a
    scrub.

    Bob
    --
    Bob Friesenhahn
    bfriesen at simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
    GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/

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