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NAS, DAS, Or What?

Comparing External RAID Housings
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The products tested in this article are pure Direct Attached Storage (DAS) devices. To be able to use a DAS device, you must be connected to a computer which has the appropriate controller. The storage capacity on the external unit is, first and foremost, only available to the user of the computer to which it is attached. To enable other users within the network to access the external storage unit, this must be explicitly made possible using the Windows Release function. DAS devices do not have an operating system, unlike Network Attached Storage (NAS) devices, which usually do.

NAS devices are not connected to a computer—they are always connected directly to the network. Access control and the configuration of the drives are taken care of by the integrated operating system, which can usually be controlled via a web interface. NAS devices are characterized by the fact that they have various RAID modes that can be used to operate several drives in a cluster. This helps to ensure that, in the event of one disk failing, the functioning of the NAS device itself is not affected.

Support for various RAID modes with NAS devices can be considered standard today, but DAS devices are increasingly also offering this functionality.

External RAID via eSATA and USB

Thanks to the intelligent SATA controller, which, alongside the port multiplier also provides a virtualization layer, multiple drives can now be addressed simultaneously in a single housing via either eSATA or USB 2.0. The operation of an external RAID cluster in the DAS devices is thus possible. To operate a RAID configuration, it is necessary for the housing to be used with at least two drives.

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