We analyze the problem of efficiently storing large amounts of data on a distributed set of servers that may be accessed concurrently from multiple clients by sending messages over an asynchronous network. Up to one third of the servers and an arbitrary number of clients may be faulty and exhibit Byzantine behavior. We provide the first simulation of a multiple-writer multiple-reader atomic read/write register using erasure-coding in this setting that achieves optimal resilience and minimal storage overhead. Additionally, we give the first implementation of non-skipping timestamps which provides optimal resilience and withstands Byzantine clients; it is based on threshold cryptography.