parvez shaikh wrote: > Hello, > > I am learning ZFS, its design and layout. > > I would like to understand how Intent logs are different from journal? > > Journal too are logs of updates to ensure consistency of file system > over crashes. Purpose of intent log also appear to be same. I hope I am > not missing something important in these concepts.
There is a difference. A journal contains the necessary transactions to make the on-disk fs consistent. The ZFS intent is not needed for consistency. Here's an extract from http://blogs.sun.com/perrin/entry/the_lumberjack : ---- ZFS is always consistent on disk due to its transaction model. Unix system calls can be considered as transactions which are aggregated into a transaction group for performance and committed together periodically. Either everything commits or nothing does. That is, if a power goes out, then the transactions in the pool are never partial. This commitment happens fairly infrequently - typically a few seconds between each transaction group commit. Some applications, such as databases, need assurance that say the data they wrote or mkdir they just executed is on stable storage, and so they request synchronous semantics such as O_DSYNC (when opening a file), or execute fsync(fd) after a series of changes to a file descriptor. Obviously waiting seconds for the transaction group to commit before returning from the system call is not a high performance solution. Thus the ZFS Intent Log (ZIL) was born. ---- > > Also I read that "Updates in ZFS are intrinsically atomic", I cant > understand how they are "intrinsically atomic" > http://weblog.infoworld.com/yager/archives/2007/10/suns_zfs_is_clo.html > > I would be grateful if someone can address my query > > Thanks > > ------------------------------------------------------------------------ > Explore your hobbies and interests. Click here to begin. > <http://in.rd.yahoo.com/tagline_groups_6/*http://in.promos.yahoo.com/groups> > > > > ------------------------------------------------------------------------ > > _______________________________________________ > zfs-discuss mailing list > zfs-discuss@opensolaris.org > http://mail.opensolaris.org/mailman/listinfo/zfs-discuss _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
