On 10 November, 2011 - Will Murnane sent me these 1,5K bytes: > On Thu, Nov 10, 2011 at 14:12, Tomas Forsman <st...@acc.umu.se> wrote: > > On 10 November, 2011 - Bob Friesenhahn sent me these 1,6K bytes: > >> On Wed, 9 Nov 2011, Tomas Forsman wrote: > >>>> > >>>> At all times, if there's a server crash, ZFS will come back along at next > >>>> boot or mount, and the filesystem will be in a consistent state, that was > >>>> indeed a valid state which the filesystem actually passed through at some > >>>> moment in time. So as long as all the applications you're running can > >>>> accept the possibility of "going back in time" as much as 30 sec, > >>>> following > >>>> an ungraceful ZFS crash, then it's safe to disable ZIL (set > >>>> sync=disabled). > >>> > >>> Client writes block 0, server says OK and writes it to disk. > >>> Client writes block 1, server says OK and crashes before it's on disk. > >>> Client writes block 2.. waaiits.. waiits.. server comes up and, server > >>> says OK and writes it to disk. > > When a client writes something, and something else ends up on disk - I > > call that corruption. Doesn't matter whose fault it is and technical > > details, the wrong data was stored despite the client being careful when > > writing. > If the hardware is behaving itself (actually doing a cache flush when > ZFS asks it to, for example) the server won't say OK for block 1 until > it's actually on disk. This behavior is what makes NFS over ZFS slow > without a slog: NFS does everything O_SYNC by default, so ZFS runs > around syncing all the disks all the time. Therefore, you won't lose > data in this circumstance.
Which is exactly what this thread is about, consequences from -disabling- sync. /Tomas -- Tomas Forsman, st...@acc.umu.se, http://www.acc.umu.se/~stric/ |- Student at Computing Science, University of Umeå `- Sysadmin at {cs,acc}.umu.se _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
