Jan Engelhardt wrote: [] > The other thing is, the bitmap is supposed to be written out at intervals, > not at every write, so the extra head movement for bitmap updates should > be really low, and not making the tar -xjf process slower by half a minute. > Is there a way to tweak the write-bitmap-to-disk interval? Perhaps > something in /sys or ye olde /proc. Maybe linux-raid@ knows 8) Hmm. Bitmap is supposed to be written before actual data write, to mark the to-be-written areas of the array as "being written", so that those areas can be detected and recovered in case of power failure during actual write. So in case of writing to a clean array, head movement always takes place - first got to bitmap area, and second to the actual data area. That "written at intervals" is about clearing the bitmaps after some idle time. In other words, dirtying bitmap bits occurs right before actual write, and clearing bits occurs at intervals. Sure, if you write to (or near) the same place again and again, without giving a chance to md subsystem to actually clean the bitmap, there will be no additional head movement. And that means, for example, tar -xjf sometimes, since filesystem will place the files being extracted close to each other, thus hitting the same bit in the bitmap, hence md will skip repeated bitmap updates in this case. /mjt - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
