On Tue, May 6, 2008 at 2:53 AM, Neil Brown <neilb@xxxxxxx> wrote: > On Wednesday April 2, snitzer@xxxxxxxxx wrote: > > resync via bitmap if faulty's events+1 == bitmap's events_cleared > > > > For more background please see: > > http://marc.info/?l=linux-raid&m=120703208715865&w=2 > > > > Without this change validate_super() will prevent the previously faulty > > member from recovering via bitmap, e.g.: > > I can't help thinking that you are misinterpreting something. I don't > think there is a clean->dirty transition happening here. > You could confirm this by using --examine on both devices after the > messy shutdown and before re-assembling the array. > > Even allowing for that possible confusion, I cannot quite see what is > going on. > It is fairly clear from the event counts that the NBD device is marked > clean, but if this is happening at array-shutdown time, I cannot see > why md would try to write to the NBD device and thereby detect an > error... > > Do you have an internal bitmap or a bitmap in an external file? > > In general, I would not like to make decisions based on the > oddness/evenness of the event counter. I consider that to be an > internal implementation detail. I am happy to make decisions based on > a difference-of-1. I need to understand the big picture first though. Hi Neil, I definitely could be misinterpreting something. However, I did determine that if the write-mostly NBD member of the raid1 becomes degraded while writing to the raid1 it frequently has an 'events' that is one less than the 'events_cleared' (of the local raid1 member that the array gets reassembled with first). The events indicate the NBD member is clean and the local member is dirty. I'm using internal bitmaps. I've focused on the even->odd (clean->dirty) transition to rationalize the safety of allowing the NBD member to be off by one _and_ clean. That could easily be superficial but it seems significant. It looks like bitmap_update_sb()'s incrementing of events_cleared (on behalf of the local member) could be racing with the fact that the NBD member becomes faulty (whereby making the array degraded). This allows the events_cleared to reflect a clean->dirty transition last occurred before the array became degraded. My reasoning is: If it was a clean->dirty transition the bitmap still has the associated dirty bit set in the local member's bitmap, so using the bitmap to resync is valid. thanks, Mike -- 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
