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From Sanjeev Neelarapu <>
Subject RE: Secondary Storage IP Subnet: Is it Optional or Mandatory?
Date Thu, 17 Oct 2013 06:53:00 GMT
Hi Rob,

Even in 4.2 defining storage traffic is not mandatory while creating physical network. If
you opt to have storage network then you have to specify IP range.


-----Original Message-----
From: Rob C. [] 
Sent: Thursday, October 17, 2013 4:58 AM
Subject: Secondary Storage IP Subnet: Is it Optional or Mandatory?


According to some (possibly old) documentation I read, I have the impression that it is *optional*
to define a secondary storage IP subnet.

Note, my questions are all in the context of:
- CloudStack 4.2
- ESXi hosts / vSphere 5.1
- Primary Storage is VMFS via fiber channel
- Advanced Networking

Here is the document to which I am referring, along with the relevant
CloudStack System VMs:
*"Network Terminology -> Storage: As it relates to CloudStack, this is an optional network
dedicated to secondary storage. If not specified, the management network will be assumed for
this role."* *"SSVM -> eth3 (storage): Note if a physical storage interface was not specified
when creating the zone this interface will not exist. Storage traffic will assume the management

My Questions:
1. Is the above-referenced document accurate for CloudStack 4.2?

2. Do I interpret correctly that I don't need to define an IP subnet for Secondary Storage?

3. I have noticed that the CloudStack 4.2 Installation Guide, section 2.8.3 "Advanced Zone
Network Traffic Types", for the type "Storage" says: *"You must configure the IP range to
use for the storage network."*
How am I to interpret the quoted statement?  Is it saying that I must configure a range regardless,
or only if I *opt* to have a Secondary Storage network?  If there is no Secondary Storage
IP subnet, would I enter a range selected from the Management IP subnet?

I am aware of the redundancy and performance benefits to using separate interfaces, this is
not my concern here.  My idea is to have a simplified CloudStack architecture by using a single
IP subnet for CloudStack Management, and putting the NFS server on the same subnet (NFS to
be used for Secondary Storage only).

If your response is that a defined Secondary Storage IP subnet is a mandatory requirement,
then I have a few other questions regarding this
4. I haven't found any documentation that helps with planning the size of the Secondary Storage
network -- besides the NFS server and the SSVM, what other devices must have an IP address
on this network?

5. How are IP addresses for devices on the Secondary Storage network assigned?  In the case
of the SSVM it must be dynamic, but if I were to manually put a CloudStack host onto this
network (for convenience), what assures that the same IP address won't also get handed out
to an SSVM?

6. Is it permitted to place the Secondary Storage traffic onto its own dedicated vSwitch on
ESXi?  According to the Installation Guide under section Separating Traffic: "*CloudStack
allows you to use vCenter to configure three separate networks per ESXi host. *...*  The allowed
networks for configuration are public, guest, and private (for management and usually storage
traffic).*"  This would suggest that storage traffic must share the same vSwitch as management

If I am missing something fundamental, and/or asking the wrong questions, please correct me!
 Same goes if you have some general insight into the pros and cons of having a Secondary Storage
IP subnet.

Many thanks!

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