On Wed, 7 Apr 2010, Edward Ned Harvey wrote:
From: Ragnar Sundblad [mailto:ra...@csc.kth.se]
Rather: ... >=19 would be ... if you don't mind loosing data written
the ~30 seconds before the crash, you don't have to mirror your log
device.
If you have a system crash, *and* a failed log device at the same time, this
is an important consideration. But if you have either a system crash, or a
failed log device, that don't happen at the same time, then your sync writes
are safe, right up to the nanosecond. Using unmirrored nonvolatile log
device on zpool >= 19.
The point is that the slog is a write-only device and a device which
fails such that its acks each write, but fails to read the data that
it "wrote", could silently fail at any time during the normal
operation of the system. It is not necessary for the slog device to
fail at the exact same time that the system spontaneously reboots. I
don't know if Solaris implements a background scrub of the slog as a
normal course of operation which would cause a device with this sort
of failure to be exposed quickly.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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