[dm-devel] dm-multipath has great throughput but we'd like more!

[Bob Gautier <rgautier redhat com>]

Yesterday my client was testing of multipath load balancing and failover
on a system running ext3 on a logical volume which comprises about ten
SAN LUNs all reached using multipath in multibus mode over two QL2340
HBAs.

On the one hand, the client is very impressed: running bonnie++
(inspired by Ronan's GFS v VxFS example) we get just over 200Mbyte/s
over the two HBAs, and when we pull a link we get about 120MByte/s.

The throughput and failover response times are better than the client
has ever seen, but we're wondering why we are not seeing higher
throughput per-HBA -- the QL2340 datasheet says it should manage
200Mbyte/s and all switches etc. run at 2GBps.

Any ideas?

Bob Gautier
+44 7921 700996