The storage didn't answer, or asked to wait. Try again later.
Adapters return it for a timeout, a closed connection, a server error, throttling and too many open files. It's the
only error where retrying may help. Fil doesn't retry (for now), because only the caller knows whether a failed
mutation is safe to repeat.
Summary
Types
@type t() :: %Fil.UnavailableError{ __exception__: term(), disk: Fil.Disk.t() | nil, op: Fil.Op.name() | nil, path: String.t() | nil, reason: term() }