On 12/06/09 10:11, Anurag Agarwal wrote:
Hi,
My reading of write code of ZFS (zfs_write in zfs_vnops.c), is that all
the writes in zfs are logged in the ZIL.
Each write gets recorded in memory in case it needs to be forced out
later (eg fsync()), but is not written to the on-disk log until then
or until the transaction group commits which contains the write
in which case the in-memory transaction is discarded.
And if that indeed is the case,
then yes, ZFS does guarantee the sequential consistency, even when there
are power outage or server crash. You might loose some writes if ZIL has
not committed to disk. But that would not change the sequential
consistency guarantee.
There is no need to do a fsync or open the file with O_SYNC. It should
work as it is.
I have not done any experiments to verify this, so please take my
observation with pinch of salt.
Any ZFS developers to verify or refute this.
Regards,
Anurag.
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