Hi I have tried to understand how RAID5 works in linux-3.6.4 by tracing the raid5.c in md driver. After days of work on the source code, I get confused by the error correction and bad block tracking mechanism. I try to come up with some conclusions, but I don't know if I am right or not. Here's my findings these days, hope someone could correct me if I am wrong. In RAID5, the bad block will be identified and register to upper layer under two conditions: 1. When read error occurs, we success to rewrite the data back but fail to re-read it back 2. When write error occurs Since write error is critical, we prevent the error disk from being written again, which makes the bad block registered by write errors impossible to be corrected again. On the other hands, the following read or write on the known bad blocks registered by read errors could possibly make bad block "good" again, and then we can unregister these bad blocks. Therefore, comparing to older version of md, the benefit of introducing bad block tracking into RAID5 is that we reserve the possibility that a read error block could still be corrected by following read/write. (In older version, the code simply called md_error when re-read still fails upon a read error) Thanks for your patience. Any help would be grateful Dennis -- 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
