Best way to deploy Backup domain controller?

Hello Experts,
we have a client network and are about to install a new physical domain controller server 2012. We would like to create a backup domain controller as well , perhaps using one of there older decommissioned servers. Will having a physical primary DC work alongside  a virtual backup DC. What softawre should we be considering pleasE?
also general question, client has office 365 but the 50 odd users access the fileserver onsite (which is part of the DC). Do we need users CALs for filesharing?
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All of your servers should be virtual. There is no reason to deploy a physical server, especially if it is a domain controller and/or file server. Virtual servers are easier and cheaper to backup, migrate, adjust disk sizes, etc. They also boot much faster, among other benefits.

At least two of your domain controllers should be full writable domain controllers, and they should also be global catalog servers. Keeping them on separate hosts is a good idea.

When configuring DHCP, use the new DHCP failover feature in Windows 2012.

Every person who accesses your server in any way needs a Windows Server CAL. So yes, all 50 users would need a CAL in addition to the Office 365 fees.

FYI, backup domain controllers don't exist in Active Directory environments. BDC is a relic of Windows NT that didn't carry forward.

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unrealone1Author Commented:
thanks for this, the customer wants the primary to be hardware, so on that basis how is it best to setup
 create a virtual backup domain controller alongside the physical dc please?
Jian An LimSolutions ArchitectCommented:
you can create a backup domain controller in another phsyical or virtual server as long as it is not on the same hardware on the primary (defeat the purpose of having backup)

The virtual world seems to take off as Windows 2012 provide additional virtual licence, and virtual box is easier to backup (but do you really need to backup AD?)
OP, are you familiar with having multiple DCs in an environment?
unrealone1Author Commented:
Great advise from the experts, thankyou
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