Hi - Nikita''s discussion is excellent. I read through and thought about this a bit over the vacation. Two important issues remain unclear in my mind: 1. the write back cache mode is not good for scaling (eg. for many nodes creating files in one directory); for that intents save a lot of RPCs. The recovery correctness discussion doesn''t cover this, and I''ve found this to introduce new opportunities for cascading aborts, that are not managed by client locks. I think it would be most beautiful if the epoch protocol was somewhat enhanced to also handle intent style processing (where there is dependence on RPC responses). I think some of the response data (FIDs notably) is not protected by locks (as it is immutable). 2. I''m nervous about broadcasting epoch messages to, for example, 1 million clients (I think that is the current target). You''d want a tree model for this, and do careful calculations how often failures will occur and what their impact is on recovery time. Peter -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.lustre.org/pipermail/lustre-devel/attachments/20090109/1c387527/attachment.html