We’re emulating some in-disk algorithms in a device mapper target, and would like to be able to do a fair comparison between the emulated and real versions; however they see radically different I/O streams, evidently because there’s no scheduling / request merging / etc. on top of the bio-based device mapper target. It appears that if our device mapper were request-based instead of bio-based we wouldn’t have this issue, but after reading a bunch of history on the mailing list archives I don’t think this is going to happen easily. Does anyone have any thoughts on quick-and-dirty ways to approximate this so we can get some preliminary measurements? dm-multipath won’t stack on a bio-based target, and attempts to stack loopback and various iscsi targets on top haven’t achieved the desired results. (in general these have resulted in our dm target seeing individual 4K I/Os, instead of the larger I/Os at the higher layer) Thanks, ..................................................................... Peter Desnoyers pjd@xxxxxxxxxxx Northeastern Computer & Information Science -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
