I have Orthanc installed on a server with Windows Server 2012. I store the patient information on a NAS that is installed on the network but I keep the index files on the server's hard drive, this allows me two things, the first solve the limitation of 2TB of Windows and the second, access to the data in a very fast way (if I install the data and the indexes in the NAS it takes longer to access).
In my case, my orthanc.json configuration file has this configuration declared in the "StorageDirectory" and in the "IndexDirectory" (data on the NAS and indexes on disk C of the server):
"StorageDirectory": "\\\\ synology \\ share4 \\ orthanc",
"IndexDirectory": "C: \\ Orthanc",
Just for reference. I have 4 Orthanc servers on the same network with almost 300,000 studies stored and together they occupy 11TB of storage on a NAS. I have several studies stored, from Rx studies that occupy a few megabytes to tomographies that occupy several gigabytes and the maximum delay I have when I look for the information of a patient, in all servers, is 7 seconds. If I needed to reduce that search time even more, I could swap my hard drives for SSDs.
I hope this information is helpful to you
William