On Fri, 2 Apr 2010, Edward Ned Harvey wrote:
were taking place at the same time. That is, if two processes both complete
a write operation at the same time, one in sync mode and the other in async
mode, then it is guaranteed the data on disk will never have the async data
committed before the sync data.
Based on this understanding, if you disable ZIL, then there is no guarantee
about order of writes being committed to disk. Neither of the above
guarantees is valid anymore. Sync writes may be completed out of order.
Async writes that supposedly happened after sync writes may be committed to
disk before the sync writes.
You seem to be assuming that Solaris is an incoherent operating
system. With ZFS, the filesystem in memory is coherent, and
transaction groups are constructed in simple chronological order
(capturing combined changes up to that point in time), without regard
to SYNC options. The only possible exception to the coherency is for
memory mapped files, where the mapped memory is a copy of data
(originally) from the ZFS ARC and needs to be reconciled with the ARC
if an application has dirtied it. This differs from UFS and the way
Solaris worked prior to Solaris 10.
Synchronous writes are not "faster" than asynchronous writes. If you
drop heavy and light objects from the same height, they fall at the
same rate. This was proven long ago.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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