On Fri, May 22, 2009 7:13 pm, Xu Yuehai wrote: >> >> If chunk_aligned_read results in an error, then the request >> is re-tried through the stripe cache. I would call that "error >> handling". > > I think you mean that error() and raid5_align_endio are invoked and > the read request is sent to conf->retry_read_aligned_list, then the > raid5d will handle it. Yes, that sounds right. > >> If the cache finds that a drives is failed, the data is calculated >> from the other drives, though the code is not a straight forward >> as it used to be. >> See fetch_block5 which sets STRIPE_OP_COMPUTE_BLK which causes >> ops_run_compute5 to do the work (or to schedule the work on separate >> hardware). >> > I notice that the bit STRIPE_OP_COMPUTE_BLK is set if only s->uptodate > == disks - 1, however, suppose there is just a single read request, I > fail to find out why this condition is satisfied. If there is just one read for a block on a device that has failed, then fetch_block5 will schedule read requests (Wantread) on all the other devices. Once all those reads complete Uptodate will be set, so s->update will indeed equal disks - 1, and so COMPUTE_BLK will get set. 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
