For EQL w/o a doubt FC should be enabled.   Flowcontrol is only active when a server or switch asks for it.  Otherwise it's not used.  The EQL array will not send a request for FC, but it will respond to one if requested.   So it does no harm to enabled it.  If you are getting excessive FC requests that usually points to an issue with your switch.  Possibly lack of port buffers to handle the load for example.     Also,  when disabled you may not notice it during normal IO, since it may not be active often.  But during replication or backups with such sustained reads, we commonly see servers request FC since the buffers the OS allocates aren't sufficient for a sustained sequential load.     So if your IO load or testing load doesn't push a server to the point it can no longer handle the load, then FC is a passive and doesn't do any harm.  But if it's not available, then re-transmissions creep in.  If that becomes bad enough, performance plummets and connections can be dropped. 
Hi, we do use a huge ammount of eql arrays, in our primary datacenter only 10gb ones (6 x 6510, 2 x 6110). Now: We often do performance tests in our lab and especially with 10 gb we saw no advantage in using flow control anymore (os: esxi 5, hardware: dell r720s, r710s, 810s, switches: dell 8024s, nics: intel x520 da2). BUT anyhow, as is is recommended by eql, we still set it all active in the production environment.Now: Aside from the fact that we only use eql, we still do "monitor" the recommendations of other storage vendors with iSCSI methods. So we came across a brand new whitepaper from netapp, dated may 2012: [URL] (see page 104) which suddenly recommends to DISABLE flow control, especially with 10 gb networks. I found that very interesting because they ALWAYS insited on flow control (even stronger than eql is insisting on them). Now they suddenly go back saying nowadays with up-to-date networking equipment it´s better to disable em, especially with 10 gb.  So, my question would be: Is the 2012 equallogic recommendation to disable flowcontrol, too OR is the recommendation still to enable it? Best regards,Joerg PS: Nope, this question is not about DCB, it´s just about "normal" flow control.
flow control in 10gb environments