On 26.08.2011 01:01, Gregory Maxwell wrote: > On Wed, Aug 24, 2011 at 9:11 AM, Berend Dekens <bt...@cyberwizzard.nl> wrote: > [snip] >> I thought the idea of COW was that whatever happens, you can always mount in >> a semi-consistent state? > [snip] > > > It seems to me that if someone created a block device which recorded > all write operations a rather excellent test could be constructed > where a btrfs filesystem is recorded under load and then every partial > replay is mounted and checked for corruption/data loss. > > This would result in high confidence that no power loss event could > destroy data given the offered load assuming well behaved > (non-reordering hardware). If it recorded barrier operations the a > tool could also try many (but probably not all) permissible > reorderings at every truncation offset. >
I like the idea. Some more thoughts: - instead of trying all reorderings it might be enough to just always deliver the oldest possible copy - the order in which btrfs writes the data probably depends on the order in which the device acknowledges the request. You might need to add some reordering there, too - you need to produce a wide variety of workloads, as problems might only occur at a special kind of it (directIO, fsync, snapshots...) - if there really is a regression somewhere, it would be good to also include the full block layer into the test, as the regression might not be in btrfs at all - as a first small step one could just use blktrace to record the write order and analyze the order on mount as well > It seems to me that the existence of this kind of testing is something > that should be expected of a modern filesystem before it sees > widescale production use. > -- -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
