On Aug 24, 2009 09:34 -0400, Theodore Ts'o wrote: > On Mon, Aug 24, 2009 at 10:33:10AM +0200, Christian Fischer wrote: > > I try to figure out reasonable mount options for ext4. > > > > I've seen a "Enable asynchronous commits by default" patch from Sun, 21 Sep > > 2008. > > > > Why is it revoked? > > It patch was never merged because the ayschronous commits feature > disabled all write barriers, so under heavy workloads a power failure > could cause data loss. > > No one has gotten around to looking at this closely; I think adding a > strategically placed blkdev_issue_flush() will allow us to safely > enable this feature, but it needs careful study. I don't think that was the issue, but rather that we wanted to have per-block checksums in order to handle the case were some block in transaction A is causing a transaction checksum failure, yet transaction B has already committed and begun checkpointing. One option discussed was to add a lightweight 16-bit checksum (e.g. TCP checksum) to the high bits of the t_flags of the block tag. The checksum doesn't have to be very strong since the whole-transaction checksum will be the primary point of validation. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
