On Sat, May 2, 2009 3:55 am, Mario 'BitKoenig' Holbe wrote: > On Fri, May 01, 2009 at 12:11:43PM +1000, Neil Brown wrote: >> There some other places >> where are are overflowing on a shift. One of those (in >> bitmap_dirty_bits) can cause the problem you see. >> This patch should fix it. Please confirm. > > Together with the small syntax-fix attached this patch fixes the > allocation of half of the available pages only. Now, all pages are > allocated when I set all bits and they all get cleaned in-kernel as well > as on-disk. Good. Thanks for the confirmation (and fix). > > However, can you confirm that the bitmap is really used in raid10 > resync? I removed half of the disks (a correctly removable subset, of > course :)), copied 100G to the degraded array, got about 7k bit set in > the bitmap, (re-)added the removed devices (mdadm correctly states > re-add as well), but the resync looks *very* sequential. > Moreover: I stopped and re-assembled the array with about 2k bit left > set and the resync starts from the beginning, I can see no skip to the > previous position in the resync process. > I'll try to watch this and will trigger you again when I have more > stable evidence, but perhaps you have some faster test-cases, I have to > wait for at least 5 hours now :) I just did some testing and it does seem to honour the bitmap during recovery. However there are some caveats. 1/ it processes the whole array from start to finish in chunk-sized blocks and simply doesn't generate IO where it isn't needed. This is different to e.g. raid1 where it can skip over a whole bitmap-chunk at at time. So it does use more CPU 2/ With raid1, when it skips a whole bitmap chunk, that chunk is not included in the speed calculation. With raid10, everything is included. So I found the resync was hitting the limit of 200M/sec and backing off. I increased the limited (Added a few more zeros) and it sped up. 3/ I found a bug. If you have two devices missing and add just one, then after the recovery it might clear the bitmap even though there is another missing device. When that device is re-added, it will be added with no recovery. This is bad. I'll post a patch shortly. What speed are (were) you getting for resync. If it was around 200M/sec, then point 2 would explain it. If it was closer to the device speed, then there must be something else going wrong. NeilBrown -- 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
