Miles Nordin wrote: >>>>>> "mo" == Mertol Ozyoney <[EMAIL PROTECTED]> writes: >>>>>> > > mo> One of our customer is suffered from FS being corrupted after > mo> an unattanded shutdonw due to power problem. > > mo> They want to switch to ZFS. > > mo> From what I read on, ZFS will most probably not be corrupted > mo> from the same event. > > It's not supposed to happen with UFS, either. nor XFS, JFS, ext3, > reiserfs, FFS+softdep, plain FFS, mac-HFS+journal. All filesystems in > popular use for many years except maybe NTFS are supposed to obey > fsync and survive kernel crashes and unplanned power outage that > happens after fsync returns, without losing any data written before > fsync was called. The fact that they don't in practice is a warning > that ZFS might not, either, no matter what it promises in theory. >
There is a more common failure mode at work here. Most low-cost disks have their volatile write cache enabled. UFS knows nothing of such caches and believes the disk has committed data when it acks. In other words, even with O_DSYNC and friends doing the "right thing" in the OS, the disk lies about the persistence of the data. ZFS knows disks lie, so it sends sync commands when necessary to help ensure that the data is flushed to persistent storage. But even if it is not flushed, the ZFS on-disk format is such that you can recover to a point in time where the file system is consistent. This is not the case for UFS which was designed to trust the hardware. -- richard _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
