Currently, when an OSD journal is stored as a file, we preallocate it as a large contiguous extent. That means that for every journal write we're seeking back to wherever the journal is. That possibly not ideal for writes. For reads it's great, but that's the last thing we care about optimizing (we only read the journal after a failure, which is very rare). I wonder if we would do better if we: 1- trim/discard the old journal contents, 2- posix_fadvise RANDOM I'm not sure what the XFS behavior is in this case, but ideally it seems what we want it to do is write the journal wherever on disk it is most convenient... ideally contiguous with some other write that it is already doing. If fadvise random doesn't do that, perhaps there is another allocator hint we can give it that will get us that behavior... sage -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
