2010/2/5 Matthew Dillon <dil...@apollo.backplane.com> > :Btw, that should be already possible using multiple HAMMER volumes. > :The SSD partition should be made the root volume. It can be very > :small, so that only the UNDO log fits on it (maybe a GB?), the second > volume > :would then be the regular hard disk. Maybe we'd need to give newfs_hammer > :a specific option so that it treats all space of the first volume as UNDO > :and > :uses the second volume for storage. > : > :I think I can implement that. Matt, do you think the option to > newfs_hammer > :is > :a good idea? > : > :Regards, > : > : Michael > > Not for newfs_hammer. It would be a good fit for the hammer > volume-add directive, though. >
Okay, I was just thinking about the lowest hanging fruit, and changing a few lines in newfs_hammer (basically just the space calculations) seemed to be those fruits :) > > You could add a feature where it adds the volume and moves the > UNDO FIFO into it. volume-del might also have to be adjusted to > move the UNDO FIFO back out (I don't recall offhand if it moves > UNDO blocks). > It doesn't move UNDO yet. Right now, the UNDO log is always on the root volume, but when we add another volume, we allocate the same space on the new volume for the UNDO log. So at least we are well prepared for moving the UNDO. Your idea sounds good, and would lead us to one step closer to root volume removal. Could I implement moving the UNDO log by flushing everything to disk, so that the UNDO log gets empty and then simply switching the log to the new one? IIRC, writing an UNDO entry required the root volume to be updated in HAMMER versions <= 3, which is no longer true as of V4. Regards, Michael
