Not quite, though that's part of what the problem was. There's a mechanism (fsync) for forcing the changes in a particular file to be written to disk. As a result of the consistency guarantees made by the "data=ordered" mode, synchronizing a single file often forces the filesystem to make other, unrelated writes to the disk as well. In the worst case the entire cache can be forced to disk. The end result is substantially more disk activity than would be expected.