HDFS backing storage is useful for following scenarios.
1. For Hadoop clusters which don't run HBase.
2. For fallback from HBase when HBase cluster is temporary unavailable. Quoting ATS design document of
In the case the HBase
storage is not available, the plugin should buffer the writes temporarily (e.g. HDFS), and flush
them once the storage comes back online. Reading and writing to hdfs as the the backup storage
could potentially use the HDFS writer plugin unless the complexity of generalizing the HDFS
writer plugin for this purpose exceeds the benefits of reusing it here.