Dennis Clarke writes: > > > On Mon, Jan 08, 2007 at 03:47:31PM +0100, Peter Schuller wrote: > >> > http://blogs.sun.com/roch/entry/nfs_and_zfs_a_fine > >> > >> So just to confirm; disabling the zil *ONLY* breaks the semantics of > >> fsync() > >> and synchronous writes from the application perspective; it will do > >> *NOTHING* > >> to lessen the correctness guarantee of ZFS itself, including in the case > >> of a > >> power outtage? > > > > That is correct. ZFS, with or without the ZIL, will *always* maintain > > consistent on-disk state and will *always* preserve the ordering of > > events on-disk. That is, if an application makes two changes to the > > filesystem, first A, then B, ZFS will *never* show B on-disk without > > also showing A. > > > > So then, this begs the question Why do I want this ZIL animal at all? >
You said "correctness guarantee" Bill said "...consistent on-disk state" The ZIL is not necessary for ZFS to keep it's on-disk format consistent. However the ZIL is necessary/essential to provide synchonous semantics to application. Without a ZIL fsync() and the like become a NO-OP; it's a very uncommon requirement altough one that does exists. But for ZFS to be a correct Filesystem, the ZIL is necessary and provides an excellent service. My article shows that ZFS with the ZIL can be better than UFS (which uses it's own logging scheme). -r _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
