Ja S wrote: > --- Christine Caulfield <ccaulfie@xxxxxxxxxx> wrote: > >> Ja S wrote: >>> Hi, All: >>> >>> >>> When an application on a cluster node A needs to >>> access a file on a SAN storage, how DLM process >> the >>> lock request? >>> >>> Should DLM firstly determine whether there already >>> exists a lock resource mapped to the file, by >> doing >>> the following things in the order 1) looking at >> the >>> master lock resources on the node A, 2) searching >> the >>> local copies of lock resources on the node A, 3) >>> searching the lock directory on the node A to find >> out >>> whether a master lock resource assosicated with >> the >>> file exists on another node, 4) sending messages >> to >>> other nodes in the cluster for the location of the >>> master lock resource? >>> >>> I ask this question because from some online >> articles, >>> it seems that DLM will always search the >> cluster-wide >>> lock directory across the whole cluster first to >> find >>> the location of the master lock resource. >>> >>> Can anyone kindly confirm the order of processes >> that >>> DLM does? >>> >> >> This should be very well documented, as it's common >> amongst DLM >> implementations. >> > > I think I may be blind. I have not yet found a > document which describes the sequence of processes in > a precise way. I tried to read the source code but I > gave up due to lack of comments. > > >> If a node needs to lock a resource that it doesn't >> know about then it >> hashes the name to get a directory node ID, than >> asks that node for the >> master node. if there is no master node (the >> resource is not active) >> then the requesting node is made master >> >> if the node does know the master, (other locks on >> the resource exist) >> then it will go straight to that master node. > > > Thanks for the description. > > However, one point is still not clear to me is how a > node can conclude whether it __knows__ the lock > resource or not? A node knows the resource if it has a local copy. It's as simple as that. -- Chrissie -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
