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[Cluster-devel] New cluster mirror log implementation (RFC)



I've started on the rewrite for the cluster mirror log (can be found in CVS head in cluster/cmirror-kernel). The purpose is to bring it inline with the new CMAN/OpenAIS framework. Since this framework is now in user-space, the cluster mirror log server implementation will exist in user-space.

I've only worked on the client side (kernel) code so far. I plan to use netlink to communicate requests from the client (kernel) to the server (user-space). The server will be responsible for coordinating cluster events, responding to client request, handling disk commits, and notifying the kernel of any log device related failures.

The server will listen to requests from the client (netlink) and send them to the rest of the cluster via OpenAIS. The results will be replicated on each machine (running the server) with the server that has the lowest cluster id responsible for committing the data to the log device.

There are 17 types of client functions - most of which will need some communication with the server. The input and output data varies. I don't want to create unique structures to pass between the client and server for each type of request, so right now I plan on passing generic data. The server will interpret the data based on the request type. The part I don't like about this plan is it requires both the client and server to be able to interpret the data correctly without the help of a header file... I can keep them in sync and check for version mismatches during the log creation phase easily enough, but perhaps there are better ideas.

Now that there are source files in-place, I'll try to submit patches to this list before committing them. When I start work on the server side, I'll probably do an initial commit and post patches thereafter (unless people would prefer I submit the opening files here first).

 brassow

For those that don't know: Logging implementations are modular and use the APIs found in linux/drivers/md/dm-log.h. Primarily, the logging implementations are used by device-mapper mirroring. Right now, there are only single machine logging implementations in the kernel. Red Hat has a cluster logging implementation for RHEL4 (cvs co -r RHEL4 cluster/cmirror-kernel), but since the upstream cluster infrastructure is based on userspace CMAN/OpenAIS, that implementation will likely not live outside of RHEL4.


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