md-cluster: Use a small window for raid10 resync
Suspending the entire device for resync could take too long. Resync in small chunks. cluster's resync window is maintained in r10conf as cluster_sync_low and cluster_sync_high, and processed in raid10's sync_request(). If the current resync is outside the cluster resync window: 1. Set the cluster_sync_low to curr_resync_completed. 2. Set cluster_sync_high to cluster_sync_low + stripe size. 3. Send a message to all nodes so they may add it in their suspension list. Note: We only support "near" raid10 so far, resync a far or offset raid10 array could have trouble. So raid10_run checks the layout of clustered raid10, it will refuse to run if the layout is not correct. With the "near" layout we process one stripe at a time progressing monotonically through the address space. So we can have a sliding window of whole-stripes which moves through the array suspending IO on other nodes, and both resync which uses array addresses and recovery which uses device addresses can stay within this window. Signed-off-by: NGuoqing Jiang <gqjiang@suse.com> Signed-off-by: NShaohua Li <shli@fb.com>
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