On Sat, Sep 11, 2010 at 1:09 AM, Neil Brown <neilb@xxxxxxx> wrote: > On Sat, 11 Sep 2010 00:58:21 -0400 > Mike Hartman <mike@xxxxxxxxxxxxxxxxxxxx> wrote: > >> > If you add a bitmap (mdadm --grow /dev/md0 --bitmap=internal) after the >> > current resync finished, then any subsequent resync due to an unclean >> > shutdown will be much faster. >> >> I read somewhere (I think in the wiki) that an intent bitmap only >> works properly on ext2 and ext3 and can cause trouble on other file >> systems. Can I use one on ext4 (what I'm using)? I'm hoping/assuming >> what I read just predates the common use of ext4. > > That is completely wrong. An intent bitmap works properly no matter what > filesystem is on top. > It does impose a small performance penalty for writes which is very > work-load-dependant, and it is not impossible that different filesystems > would suffer more or less from this, but I doubt you would notice. > > If you can find it again let me know and I'll try to get it fixed. I found it. Looks like I misremembered what it said though - it's referring to external bitmaps only. In the man page: "Note: external bitmaps are only known to work on ext2 and ext3. Storing bitmap files on other filesystems may result in serious problems." Thanks again! > >> >> Will I need to remove the bitmap before adding another disk and >> growing the array to use it? If I don't, will it speed up that >> operation any? > > You, you will need to remove the bitmap before growing the array. I really > should fix that but it doesn't seem to rise to the top of my to-do list... > > And no, a bitmap would have no effect on a reshape operation even if it were > allowed to be present. > > 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
