> > > Does ZFS recover all file system transactions which > it returned with success > > since the last commit of TxG, which implis that ZIL > must flush log records for > > each successful file system transaction before it > returns to caller so that > t can replay > > the filesystem transactions? > > Only synchronous transactions (those forced by > O_DSYNC or fsync()) are > written to the intent log. > Could you help me to clarify on "writing 'synchronous' transactions to the log"?
Assume a scenario where a sequence of new subdirectories D1, D2 (as child of D1) have been created, then new files F1 in D1 and F2 in D2 have been created, and after some writes to F1 and F2, fsync(F1) was issued. Also , assume a file F3 in other parts of the file system that are being modified. To recover F1, creation of D1 and D2 must be recovered. It would be painful to find and log the relevant information at the time of fsync() to recover them. It means that 1) ZFS needs to log EVERY (vs "synchronous") file system transactions to replay (i.e., redo onto the on-disk state of last commit of TxG) since one cannot predict when fsync() would be requested for which file, i.e., ZFS log them all in-memory, but flushes only at synchronous transaction? It also means ZFS log user data for for every write()? 2) If the cumulated log records up to fsync(F1) (from last fsync()) is flushed to disk for replay at subsequent recovery, ZFS recovers the consistent file system state at the point in time of latest fsync(), including all successful file system transaction up to that point that have nothing to do with F1, e.g., F3, before crash"? Or, am I missing something? I presume that flush of log occurs also at every write() of file opened with O_DSYNC. Otherwise, it should be same as fsync() case. Are there any other synchronization request that forces in-memory log? As a side question, does ZFS log atime update (and does snapshot copy-on-write for it)? Again, thank you for your time. This message posted from opensolaris.org _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
