I have a SAN that replicates traffic across a 100mb MAN that I need to shape back. I created a policy that guarantees 50mb and shapes to 70mb. The mirrors broke.
We're going to contact the vendor tomorrow to see WHY it couldn't work on 50mb, but I wanted to post my policy to see if there were any changes that you would make:
description Connects to the OpteMAN DR link
ip address 172.27.1.2 255.255.255.0
service-policy output DR
class-map match-all SANTRAFFIC
match access-group name SANTRAFFIC
Extended IP access list SANTRAFFIC
10 permit ip 10.131.100.0 0.0.0.255 10.131.1.0 0.0.0.255 (16427 matches)
shape peak 71680
I'm not sure if I should shape or police it, but I figured that I didn't want to just drop the traffic.
If your SAN only sends the bulk of traffic in one direction, and there's congestion, that's where you want to apply QoS (i.e. you likely could get by with application of just one policy on one end of the link). However, assuming the SAN might want to "recover" in the reverse direction, having the QoS policy already in place guarantees service levels when that happens.
With regard to your new policy approach, I recommend you try to think of priorities between traffic more than bandwidth allocations. Bandwidth allocations are generally only necessary when the applications really need it to work (well). Otherwise, it's more a question of what traffic is serviced first when there's congestion. Assuming other traffic has users waiting, and SAN replication does not, then we want to prioritize the other traffic over the SAN replication traffic. This can be done with a policy similar to the one in my prior post. Do note, although that sample policy effectively prioritizes non-SAN traffic over SAN traffic, you might still see SAN using 95% of the link. The important point though is, although SAN uses the bandwidth it "moves aside" for non-SAN traffic.