Shared file system access across many VMs

WHAT THIS TESTS The interviewer is checking that you reach for a managed file service for shared access and understand its performance envelope at scale.

A GOOD ANSWER COVERS For a hierarchical file system multiple instances mount at once, use a managed network file service: EFS on AWS, Filestore on GCP, or Azure Files. These speak NFS or SMB, scale capacity automatically or by tier, and give POSIX semantics so existing apps work unchanged. The challenges appear at scale. Each operation crosses the network, so latency is higher than local or block storage, which hurts chatty, latency-sensitive workloads. Throughput depends on the mode: some services scale throughput with stored data or offer a provisioned-throughput option, and bursting modes can throttle. Metadata-heavy workloads, like listing or stat-ing millions of small files, are especially slow because each is a network round trip. Consistency is generally close-to-open under NFS, so concurrent writers to the same file need application-level coordination.

COMMON WRONG ANSWERS Using a single block volume and trying to share it across instances. Expecting local SSD latency from a network file system. Ignoring that small-file and metadata-heavy workloads dominate latency. Assuming throughput is unlimited rather than tied to a mode or provisioned setting.

LIKELY FOLLOW-UPS How do bursting versus provisioned throughput modes differ. How would you speed up a small-file workload, for example by packing files. What consistency guarantees does NFS provide for concurrent writers. When would object storage be a better fit.

ONE CONCRETE EXAMPLE A media render farm of fifty instances must read shared assets and write outputs to a common tree. The team mounts a managed NFS file system on every node. They hit slow directory listings because thousands of tiny intermediate files create metadata pressure, so they switch to provisioned throughput and restructure the pipeline to write fewer, larger files, restoring acceptable performance across the fleet.