This is an updated implementation of journal guided resync, intended to be suitable for production systems. This feature addresses the problem with RAID arrays that take too long to resync - similar to the existing MD write-intent bitmap feature, we resync only the stripes that were undergoing writes at the time of the crash. Unlike write-intent bitmaps, our testing shows very little performance degredation as a result of the feature - around 3-5% vs around 30% for bitmaps. This feature is based on work described in this paper: http://www.usenix.org/events/fast05/tech/denehy.html As a summary, we introduce a new data write mode known as declared mode. This is based on ordered mode except that a list of blocks to be written during the current transaction is added to the journal before the blocks themselves are written to the disk. Then, if the system crashes, we can resync only those blocks during journal replay and skip the rest of the resync of the RAID array. The changes consist of patches to ext3, jbd, MD, and the raid456 personality. These patches are currently against the RHEL 5 kernel 2.6.18-128.7.1. Porting to ext4/jbd2 and a more modern kernel is a TODO item. Changes since the previous set of patches: I have addressed all review comments received. Noteable is a design change based on Neil Brown's suggestions: the filesystem now sets a buffer flag (fs_raidsync) to inform MD that the filesystem is taking responsibility for resyncing parity on this stripe in the event of a system crash. For RAID 4/5/6, setting this flag causes the write intent bitmap NOT to be updated for the write in question. There is also a buffer flag (syncraid) used by jbd to resync parity. Together these eliminate most of the need for ioctls, though one is still needed for e2fsck. Unfortunately, we have determined that these patches are NOT useful to Lustre. Therefore I will not be doing any more work on them. I am sending them now in case they are useful as a starting point for someone else's work. Cheers, Jody -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
