On Fri, 2 Apr 2010, Edward Ned Harvey wrote:
So you're saying that while the OS is building txg's to write to disk, the OS will never reorder the sequence in which individual write operations get ordered into the txg's. That is, an application performing a small sync write, followed by a large async write, will never have the second operation flushed to disk before the first. Can you support this belief in any way?
I am like a "pool" or "tank" of regurgitated zfs knowledge. I simply pay attention when someone who really knows explains something (e.g. Neil Perrin, as Casper referred to) so I can regurgitate it later. I try to do so faithfully. If I had behaved this way in school, I would have been a good student. Sometimes I am wrong or the design has somewhat changed since the original information was provided.
There are indeed popular filesystems (e.g. Linux EXT4) which write data to disk in different order than cronologically requested so it is good that you are paying attention to these issues. While in the slog-based recovery scenario, it is possible for a TXG to be generated which lacks async data, this only happens after a system crash and if all of the critical data is written as a sync request, it will be faithfully preserved.
Bob -- Bob Friesenhahn bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/ _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
