On Wed, Sep 27, 2006 at 11:17:00AM +0200, Jan Blunck wrote: > We discussed some of the ideas about snapshots here at the dm summit. The > general ideas are as follows: > > - one exception store per origin device that is shared by all snapshots > - don't keep the complete exception tables in memory all the time > - limit kcopyd outstanding requests [snip] > target. The throughput issues should be addressed by only writing to one > exception store. The memory issues should be addressed by the changes to the I have a need fro a 'snapshot' type dm mode which has this characterstic. Eg, it leavse to origin device completely untouch by any changes. I was thinking that I'd have to code it myself from scratch as I could see any simple way of reuse the existing dm-snap code - especially since in my case the origin device will always be a physical volume (ie hda). However if I can make use of a new dm-exception-store and possibly even contribute to it this would be better. I was considering some sort of B or B+ -tree type arrangement as then we can use the buffer-cache (I'm assuming something similiar still exists after the bh -> bio rewrite but I 'm a lttle behind) to store the commonly referenced exceptions, which should keep the memory required by the tables down at times of high memory pressure. > There are still ongoing discussions about the snapshot target. It would be > nice if you have additional thoughts about this proposal. I guess it is > similar to one of your prototypes. Is this where those discussion are taking place if I want to help and particpate? TTFN -- Roger. Home| http://www.sandman.uklinux.net/ Master of Peng Shui. (Ancient oriental art of Penguin Arranging) Work|Independent Sys Consultant | http://www.computer-surgery.co.uk/ New key Fpr: 1227 ABB1 7545 77A7 6816 2D18 4EBC AA9B 8EE3 1DD3
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