If you want to spin up an Apache HadoopⓇ cluster, you need to grapple with the question of how to attach your disks. Historically, this decision has favored direct attached storage (DAS). This approach is in keeping with the fundamental Hadoop principle of moving processing to a where the data lives, thereby taking advantage of disk locality to optimize performance. Disk locality is so core to Hadoop that virtually any description of Hadoop starts with this.
The alternative is to use network attached storage (NAS). In contrast to DAS, NAS separates the compute and storage layers so that storage can be shared across a number of servers by shipping data over the network. Historically, this heavy dependence on the network made NAS an order of magnitude slower. Remember, the state of the art was 1GbE networks, and switches were slower and more expensive. I/O requirements for demanding Hadoop-based applications could only be met by DAS.
This is a very interesting discussion. In my limited experience, I’ve had trouble selling operations teams on DAS, given the increased ops effort required to keep a bunch of attached disks going. Hat tip Ari Amster.