Here is the relevant section from the vCX users guide. FTS is fault tolerant storage, so you can lose a disk and that only affects the datastore data on that disk. I imagine, you could also spread out the vmdks such that it might be easier to maintain a high IOPS.
Multiple RiOS Data Stores
As of RiOS v8.6, SteelHead-v models VCX5055, and VCX7055 support up to 14 RiOS data stores using FTS.
Riverbed recommends that all RiOS data stores on an appliance are the same size.
To add additional data stores, you must power off the VM.
I appreciate the reply. I wanted to clarify the specific actions required to implement the larger VMs, but I think my initial understanding is correct. We used to have disk1 for management, and disk2 for the datastore, which is resized to align with the requirements of the VM model. Now, we also have disk3 through disk9, all being 80GB, and each has to be added by editing the resources through the vSphere client. And of course, power cycling the VM so it recognises the datastores.