DAS – Direct Attached Storage

With DAS (Direct Attached Storage), the storage system is connected locally to the server via a serial point-to-point connection (P2P). This allows for very high data transfer rates while maintaining low latencies. The setup and administration of DAS storage is carried out via the respective operating system environment and requires neither complex administration units nor additional switches. Due to the lack of protocol overhead, Direct Attached Storage is very high-performance and places low demands on the hardware. This means it is always a good choice if a single server is accessing the storage.

SCSI, Serial Attached SCSI (SAS), the block-based transfer protocols ATA/ATAPI, External Serial ATA (eSATA), Firewire, Thunderbolt, USB and USB Attached SCSI (UAS) or network-based connections are generally used as the interface for DAS. In contrast to networked and shared storage systems such as NAS (Network Attached Storage) or SAN (Storage Area Network), directly connected storage is only assigned to a single server and is therefore not sharable (exception: multipath IO for dual-controller systems).

This dedicated connection over distances of a few meters to the host system and the limited expandability, which is limited by the size of the disk stack or the maximum number of slots, limits the application possibilities for Direct Attached Storage (DAS). In addition, DAS storage cannot be cascaded as desired, which is why DAS systems are only scalable to a limited extent. While the administration effort for individual DAS servers is still manageable, it increases significantly with the number of systems to be managed. Administrators should therefore be able to forecast storage requirements for the next few years as accurately as possible in order to avoid hitting performance, capacity or administration limits with today’s high data growth rates. Frequent applications for Direct Attached Storage systems include storage for databases, ERP systems or e-mail services. In larger enterprises, DAS servers are more commonly used with NAS and/or SAN installations.

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