On mer, 2006-01-18 at 23:29 +0100, Christophe Varoqui wrote: > On mer, 2006-01-18 at 16:41 -0500, David Wysochanski wrote: > > I'm wondering where the value of 1000 came from, and > > whether that's really a good default. > > > > Some preliminary tests I've run with iSCSI seem to indicate > > something lower (say 100) might be a better default, but > > perhaps others have a differing opinion. I searched the > > list but couldn't find any discussion on it. > > > I'm not really focused on performance, but this seems to be an > io-pattern dependant choice. > > Higher values may help the elevators, (right ?) thus help the seeky > workloads. Lower values may certainly benefit from lower values to > really get the paths summed bandwidth. > > Anyway, I can not back this with numbers. Any value will be fine with me > as a default, and I highlight that now you can also set per device > defaults like rr_min_io in hwtable.c > Replying to myself, I finally got the chance to challenge my sayings, and I'm proven badly wrong :/ On a StorageWorks EVA110 FC array, 2 active 2Gb/s paths to 2 2Gb/s target ports. 1 streaming read (sg_dd dio=1 if=/dev/mapper/mpath0 of=/dev/null bs=1M count=100k) : rr_min_io = 1000 => aggregated throughput = 120 Mo/s rr_min_io = 100 => aggregated throughput = 130 Mo/s rr_min_io = 50 => aggregated throughput = 200 Mo/s rr_min_io = 20 => aggregated throughput = 260 Mo/s rr_min_io = 10 => aggregated throughput = 300 Mo/s Regards, cvaroqui -- dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
