On Mon, Apr 13, 2015 at 3:33 PM, Jeff Ferland <j...@tubularlabs.com> wrote:
> Nodetool repair -par: covers all nodes, computes merkle trees for each > node at the same time. Much higher IO load as every copy of a key range is > scanned at once. Can be totally OK with SSDs and throughput limits. Only > need to run the command one node. > No? -par is just a performance (of repair) de-optimization, intended to improve service time during repair. Doing -par without -pr on a single node doesn't repair your entire cluster. Consider the following 7 node cluster, without vnodes : A B C D E F G RF=3 You run a repair on node D, without -pr. D is repaired against B's tertiary replicas. D is repaired against C's secondary replicas. E is repaired against D's secondary replicas. F is repaired against D's tertiary replicas. Nodes A and G are completely unaffected and unrepaired, because D does not share any ranges with them. repair with or without -par only covers all *replica* nodes. Even with vnodes, you still have to run it on almost all nodes in most cases. Which is why most users should save themselves the complexity and just do a rolling -par -pr on all nodes, one by one. =Rob
