On 25/04/11 10:15, Adam Hoka wrote: >> I also don't see the need of delegating every write to secondary mirror >> legs to a thread. You definitely need a synchronization thread, but I >> think you should propagate writes to each of the mirror disks from the >> same context you are in when you get the requests. > > That "thread" could be a workq (which will run in a different thread, > obviously).
I know what you mean, but I don't see why you would do it like that. You should be dispatching writes to all the mirror disks immediately and not queue them to later dispatch them for a different thread. I see no advantage to that approach, it makes things more complicated and last but not least it is also less robust. >> You mention in your proposal the following: >> "Week 8-9: Write feature tests and fix any issues encountered, test LVM >> snapshoting". >> How is that related to the project? Am I missing something? > > The mirror target is used to sync snapshot, so yes it is highly related. > My main motivation to write the mirror target support is to enable > snapshoting (this is also the reason why did my original proposal aimed > to provide less data consistency, altough now I realize that most people > would like to use the mirror target as a general RAID-1 implemtation). I'm still not sure how the mirror would work with LVM snapshots. AFAIK linux has a snapshot device mapper target to support that and I still don't see where the mirroring fits in. And yea, what we want out of this GSoC project is a good RAID-1 / mirror implementation. We have vinum, but it is overcomplicated and outdated, so the idea is to have a nice and clean RAID1 implementation as a device mapper target. Robustness/data consistency is pretty much a top priority for this. Performance can be improved using NCQ/TCQ features whenever the design works. > I cant update the proposal, I think. This melange is a bit confusing... :-) It doesn't matter, no need to update the proposal. Take it as a "if you are selected, I think you should..." discussion. Regards, Alex Hornung
