Hi Vince, If flare is initiating copy to hotspare function, 1 hotspare is fine. However, if user is manually invoking a hotspare for proactive copy, then you need to have at least 2 hotspares configured on array keeping 1 reserved for flare initiated proactive sparing.                                         
Article 7605 recommends 1 spare per 30 drive count.  And the same recommendation can be found in VNX Applied Best Practices Guide.  But I am surprised there is no mention of the Proactive Copy feature.  In a small array with only 2 DAEs (30 disks) and a single hot spare Proactive Copy would never be invoked.  As a reminder, the proactive copy rules discussed in article 184475 require >1 available hot spares.  Proactive copy seems like a good feature to enable, but is there a reason this is not mentioned in the recommendations?  
Hot Spare Count and Proactive Copy