The elasticsearch cirrus cluster is getting low on disk space. We are currently using RAID1, except on older servers, with smaller disks, where we are already using RAID0.
Given that we have enough redundancy at the cluster level (we have at least 3 copies of any shard) and that recovery is automatic (in case we loose one server, the lost shards will be recreated on a different node), it seems like a good idea to move the full cluster to RAID0. This acknowledges that loosing one server is a non event.
Note: if we reimage those servers, it might make sense to migrate to stretch at the same time (T193649).