Adam Megacz wrote:
Ah, okay. The slides I read said that in ZFS there is "no journal --
not needed" (slide #9):
http://www.opensolaris.org/os/community/zfs/docs/zfs_last.pdf
I guess the slides are out of date in light of the "ZFS Intent Log"
journal?
Yes , I can understand your confusion. Technically the intent log is not a
journal.
A journal has to be replayed to get meta data consistency of the fs.
UFS logging, EXT3 and VXFS all use journals. For perf reasons user data is
typically not logged leading to user data inconsistency.
On the other hand, the zfs pool is always consistent whether or not the
intent log is replayed.
Anyways, it all makes sense now. Without a journal, you'd need to
perform the operation on slide #11 for every fsync(), which would be a
major performance problem. With a journal, you don't need to do this.
Great work, guys...
- Thanks Adam.
- a
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