In 2004, Mr Brown wrote that read errors could be handled without reconstruction. Has this been implemented in 2.6.8? As I understand it, this is the way RAID is supposed to work. For reference, here is the post about the matter: auto-correcting read errors Write errors must always fail a device as even if there was a cable problem rather than a media problem, the drive will be inconsistant with the array after the write failure and so cannot be trusted. However read errors do not have to be fatal. If the device can over-write a bad sector, or remap to elsewhere, then it makes sense to regenerate the data from redundant info and re-write. It is important that this over-write only be attempted if it looks like a genuine single block error, rather than a more major problem such as a head crash. So, read errors should cause a retry as they currently do, but they should not immediately fail the whole drive. Rather just the block that had the error should be marked failed. A count of failed blocks per drive must be kept and if this exceed some threshold (20??) the drive is then failed. While there are failed blocks below the threshold number, the raid control thread should instigate resync on the bad addresses. If a write fails, the drive is failed. If the write succeeded, a recheck should be performed to make sure the data really is good. If this fails, the drive should be failed. But if it succeeds, the block can be marked good again. To implement this we need a small list of failed blocks and the drive on which they are failed. Any read request to blocks in this list is allowed to continue but avoid the drive in question. Any write request blocks until the status of the block is resolved. If blocks on different drives fail such that data cannot be recovered, the array must be failed. However, failed blocks on different drives at different addresses need not be a problem. If read errors are found during resync, we must assume that those blocks are the out-of-date blocks. __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com - 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
