Seneca has worked closely with OnSSI to evaluate OCC5 performance on our server builds and to understand some of the nuances.
A summary can be read here: Ocularis 5.1 Performance Guidelines.
I would agree with Eddie that 180TB at one location that takes feeds from several sites could be a disaster waiting to happen. Any large storage array WILL have a drive fail from time to time. It is a question of when...not if.
Michael is also correct in saying you need to know the bandwidth needs of your enterprise.
Depending on the bandwidth needed, you can consider the different options available.
It is important to know the way storage works in OCC5.
You assign drive letters with directories for target Zones.
You can have multiple zones and the system will use them all based on their full/busy status when new data needs to be written. Things get a little more complex if you let these Zones get filled to their allowed space because the system will start cleaning up space to make room for the new data.
This emergency cleanup will tend to drop a few frames depending on the overall loading of the system. A best practice here is to put a real 'AGE' on the data so that it can expire.
There currently is NO useful method to migrate recent video data to a targeted archive storage target. The method is to Export the database manually from the Client application.
Why do I mention this? Because writing to local storage is faster that writing to a storage unit located far away.
In terms of performance, writing to storage located inside a server system using the PCIe bus and a RAID card is the fastest. The next fastest is having a Direct Connect Storage appliance connected to a RAID card in the Recorder system. Next in line are your network connected storage appliances where the performance capabilities are defined by the overall infrastructure created for the inter-box communication.
I would favor as many local VMS servers as needed with an appropriate amount of local storage.
You would run those as Recorder only in function. The management of the entire enterprise is handled by a separate server running the Base+Core functions. If your existing OnSSI Recorders are running OK...and have local storage.... the new Management function can see them and let them be part of the hybrid infrastructure.