Yes, there is a concern in getting a bad batch, or having several drives fail all at once. Interestingly enough, while opening those 1450 anti-static cases and seeing the manufacture date of them, they were in separate batches (some with more dust on the cases than others), so we have some heterogeneous-ness on them. HDFS with its various levels of replication factors, and our backups/DR for high-value data takes care of the rest.