cloudstack fail to start primary and second storag

I use 2 hosts to establish my cloudstack cluster.All my hosts is Ubuntu 12.04 using NFSv3 and I use host1 as both the primary and secondary storage server.The management server is also in host1.I can mount host1's primary and second storage on host2,and I can access them through host2's mount points.But,when I try to add my first zone,I encountered the problem as show below,these messages can be found in my management-server.log:

2013-10-26 04:11:47,086 INFO [storage.secondary.SecondaryStorageManagerImpl] (secstorage-1:null) Unable to start secondary storage vm for standby capacity, secStorageVm vm Id : 28, will recycle it and start a new one 2013-10-26 04:11:47,086 INFO [cloud.secstorage.PremiumSecondaryStorageManagerImpl] (secstorage-1:null) Primary secondary storage is not even started, wait until next turn 2013-10-26 04:57:16,615 WARN [storage.secondary.SecondaryStorageManagerImpl] (secstorage-1:null) Exception while trying to start secondary storage vm com.cloud.exception.AgentUnavailableException: Resource [Host:1] is unreachable: Host 1: Unable to start instance due to com.cloud.agent.api.Answer cannot be cast to com.cloud.agent.api.storage.PrimaryStorageDownloadAnswer

The log suggests that cloudstack fail to access host and start primary and secondary storages.I just don't how to test wheather the host is unreachable and how to start the primary and secondary storages.

It directly results in the two system vms stopped.I want to know some clues about how this problem occurs and some methods to debug.Any help will be appreicated!

Check that you have seeded secondary storage with the system VM template.

Prepare the System VM Template from the 4.2 Install Guide

The secondary storage system VM is responsible for adding templates to secondary storage. Without it, CloudStack cannot create new templates, which is why it has to be added manually.