LUNs and virtual machines

I have HP P2000 + XenServer solution working. What I'm thinking about is how to create LUNs for 20 virtual machines. Separate LUN for every VM ? It gives me ability to backup the specific virtual machine, however 20 vm = 20 shared storages in XenCenter and moreover I'm afraid of manageability of these LUNs or am I wrong ? Or I can have one bigger LUN for 20 VMs. What is the better option?

Solution 1:

I also think you need to ask yourself a few questions which will help you decide how many LUNs you want to create and how many VMs to deploy to each:

1. What are my organization's data retention and provisioning policies?
2. What type of data will this LUN be holding (Database, Web, just operating systems)?
3. Do we anticipate any growth in data or systems (perhaps you have 3 web servers, will you be adding a 4th?) (You may have 1TB worth of database data. Could that potentially grow?)
4. What are the business goals and objectives?

For example, if I have a heavily used database server that has a long data retention policy I will create a LUN for just the database data and perhaps put the operating system VM in a bucket LUN that holds other non-intrusive/not heavily used VMs.

Make sense?

Solution 2:

I don't know anyone who creates a separate LUN for each VM, not on Xen and not on any other hypervisor. You don't want TOO many VMs per LUN (I tend to limit my ESX datastores to 500GB to ensure that not to many can go into each) but one per LUN would just be a massive headache. If you have 20 VMs maybe think about 4 or 5 LUNs and spread them out across them.