This might be a question with an obvious answer, but I'd like verification one way or the other. Does the use of O_DIRECT essentially disable delayed allocation for a given file? My simple tests show a larger degree of block fragmentation for files written using O_DIRECT than without, and on its face, this makes sense to me. This fragmentation can be removed by using fallocate() on a file before extending it with writes. (Strictly speaking, I guess the use of O_DIRECT wouldn't "disable" delayed allocation, since the blocks are allocated at the "normal" time -- when going to disk. But effectively there would be a lot less block grouping available to build large extents if each write goes to disk immediately, instead of going through the page cache.) Thanks, Curt -- 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
