On Monday March 14, lmb@xxxxxxx wrote: > On 2005-03-14T15:43:52, Neil Brown <neilb@xxxxxxxxxxxxxxx> wrote: > > Hi there, just a question about how the bitmap stuff works with > 1++-redundancy, say RAID1 with 2 mirrors, or RAID6. I assume you mean RAID1 with 3 drives (there isn't really one main drive and all the others are mirrors - all drives are nearly equal). We haven't put any significant work into bitmap intent logging for levels other than raid1, so some of the answer may be pure theory. > > One disk fails and is replaced/reattached, and resync begins. Now > another disk fails and is replaced. Is the bitmap local to each > disk? Bitmap is for the whole array, not per-disk. If there are any failed drives, bits are not cleared from the bitmap. If a drive fails then any active resync is aborted and restarted (possibly this is not optimal...). If a failed disk is re-attached, then only the blocks changed since that the array was known-good are resynced. If a new drive is added, all blocks are synced. > > And in case of RAID1, with 4 disks (and two of them resyncing), could > disk3 be rebuild from disk1 and disk4 from disk2 (as to optimize disk > bandwidth)? If two are resyncing, they will resync in step with each other so there is no point in reading from disk2 as well as disk1. Just read from disk 1 and write to disks 3 and 4. Does that answer your questions? 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
