From this guide

http://www.equallogic.com/resourcecenter/assetview.aspx?id=9259

4.2.3    Pay Attention to Spanning Tree
In our test configurations we disabled Spanning Tree Protocol (STP) on all switch ports connecting to
end devices (the server and storage controller NICs). We also enabled the “portfast” setting on those
switch ports.
Since NIC and storage controller ports are end points they cannot create loops. Thus you should
enable the ‘portfast’ setting on those switch ports instead. With port fast enabled you eliminate the STP
forwarding state delay time that occurs when a port becomes active. This will accelerate initialization
of new iSCSI sessions if ports on an existing iSCSI connection path change status. This becomes very
important in larger SAN fabric configurations with multiple hops.