How much space does a scylla pod would require to deploy scylla db in k8s?

I am trying to deploy scyllaDB as a k8s service. Currently, trying to create a cluster with 3 pods. As of now, I attached 15GB storage to each of the pod - total of 45 GB to scylla cluster.
but I am still getting below error:

root@scylla-2:/etc/scylla# scylla
FATAL: Exception during startup, aborting: std::runtime_error (Could not setup Async I/O: Resource temporarily unavailable. The required nr_event (1) exceeds the limit of request capacity in /proc/sys/fs/aio-max-nr (65536). Try increasing that number or reducing the amount of logical CPUs available for your application)

Any idea about optimum and minimum volume to be mounted to each pod?

This error is not about amount of storage required, but number of maximum aio operations, which is a kernel property.
As message suggests, you should increase /proc/sys/fs/aio-max-nr on the k8s Node.
Or use Scylla Operator where this value can be set as part of ScyllaCluster.spec.sysctls.
Setting it to 30000000 should be enough.