DAS or NAS? Make the right data storage decision for deployed systems



September 09, 2022

For many years, military system designers relied solely on direct attached storage (DAS) devices when needing to deploy data storage on military platforms. These devices are built into or directly attached to computers, such as single board computers (SBCs) on a platform. When a DAS device is in use, only the specific SBC it is connected to can access data stored at rest (DAR). With Ethernet becoming commonplace on modern platforms, network-attached storage (NAS) devices (also known as network file servers [NFS]) have emerged as an important alternative for deployed data storage. With the NAS, the stored DAR can be made available to any client device over the Ethernet network. NAS and DAS are often used in combination to meet all program, platform and application requirements. However, in cases where it makes sense to only use a DAS or NAS device, it helps to understand how they differ.

Due to the relative simplicity of a DAS, it can be much easier to deploy than a NAS device. Since a DAS device is installed in a computer or connects directly to it, the broader connectivity requirements are mitigated. However, each DAS device on the platform must be deployed, upgraded, and maintained individually, which can increase total cost of ownership (TCO). A NAS device, on the other hand, must be connected to the Ethernet network on a platform, which can initially increase the complexity and cost of deployment. Although NAS devices are generally more expensive to purchase and deploy than DAS devices, they offer more features, such as centralized data storage, which can offset the time and cost required to purchase, upgrading and maintaining multiple storage devices.

Consider using data storage devices on larger platforms where stored data may be classified at different levels – top secret, secret, or sensitive but unclassified. These different levels of data will need to be separated and access requirements will be different for each level. DAS offers the simplest approach to separating data tiers because a DAS device is connected to a single SBC. If an Ethernet network is required, the simplest approach to managing multiple levels of classification is to create physically separate networks (or enclaves) for each level of data. Each enclave will require a separate NAS that serves its own network with no connections between them. If information flow between enclaves is desired, a cross-domain solution is needed to ensure proper data flow and access standards.

A DAS appliance offers simplified integration compared to a NAS, since it can be installed directly on an SBC. The DAS device requires no separate power supply, enclosure, or structure other than a circuit board and any conduction-cooled frame. If data transport, rather than data transfer, is required, a DAS device that supports removable data cartridges such as an RMC [removable memory cartridge] card will be preferable. After the mission, the collected data can be brought back to the base station for further analysis. A DAS device would not work for such an application, as it is not easily removable.

Using a NAS device can simplify software upgrades for users. Before each mission, the current operating system [operating system] and APP [application program] for each client can be loaded over the network via a removable data cartridge. If the operating system or APP requires updating or upgrading, new software versions can be distributed to all network clients on startup, without having to remove the client or NAS from the platform. form. An added benefit of a NAS-based network boot approach is that operating system and application data can be protected with encryption, such as CsFC two-layer encryption approved by the National Security Agency (NSA ).

Network boot can also reduce SWaP [size, weight, and power] concerns because multiple DAS devices can be replaced by a single NAS device. That said, using a single NAS device for network booting can slightly increase the total system boot time compared to booting with multiple dedicated DAS devices. A local DAS device delivers the OS and application faster because only one client needs to be served, while the NAS device needs to serve all network boot clients.

[Figure 1 | Shown: the XMC-554C 3U OpenVPX storage card, an example of a rugged DAS solution; in addition, the DTS1 Data Transport System DAS is a turnkey rugged network file server.]

Steven Petric is Senior Product Manager, Data Storage, for Curtiss-Wright’s Defense Solutions Division.

Curtiss-Wright Defense Solutions • https://www.curtisswrightds.com/

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