Next Generation Storage, Version 3.0

DAS - Direct Attached Storage. These are storage devices that connect directly to the computer, like an external disk drive or RAID system. The storage device is typically accessed by a single computer, maybe two, are directly connected to the storage. Typical connections today are SCSI, SAS, USB, etc. Not usually very reliable since it is typically single controller, if it has RAID protection at all. Not very scalable capacity or performance, even if it supports multiple expansion chassis connected to a primary chassis, there is still a relatively low limit to expand. Higher maintenance costs since you manage each and every one of these type of devices individually.

NAS (Network Attached Storage) or SAN (Storage Area Network). These are devices that are shared between many computers, are controller based, with file sharing (NAS), or as carved up block devices (SAN). These are a vast improvement over DAS in that they can share storage resources with many computers. Some of the downsides however are most are NAS or SAN, not both. These devices being controller based still have limited scalability, like DAS, creating islands of storage in the data center. If you want high availability, you have to architect it, adding complication and cost to manage. Features to replicate, snapshot, thin provision, etc. tend to be expensive, if the features are even available. Scalability is costly, being controller based to increase performance you typically have to put a more powerful controller. To increase capacity you add more disk trays, but there is a limit to how many you can add, the increments to add can also be relatively large and expensive. Hardware is typically proprietary raising maintenance costs and requiring special skill sets to manage.

NAS & SAN & Clustered & Unified Management & Everything Is Included. This type of storage is in a word, "Amazing". Based on node clustering, originally developed in the high performance computing (HPC) cluster world, this type of storage offers all the high availability enterprise features at off the shelf commodity server prices. By putting all the intelligence in software and not in proprietary hardware the flexibility, features and price point is unlike anything else.