DAS vs NAS
Direct Attached Storage
Direct Attached Storage (DAS) is a device connected to a PC in the same way as an external hard drive – it can be ATA,
SATA, SAS, USB, FireWire, or Thunderbolt. Any DAS unit uses a filesystem a host PC can provide drivers for.
The filesystem of the DAS is defined and controlled by the operating system of the PC the DAS is connected to.
A DAS provides a direct access to its disk or disks in terms of sectors, just like an internal hard disk does.
The first and the most common example is a typical external hard drive.
More complicated examples are Drobo 5D and LaCie devices.
As far as data recovery goes, the techniques applied to DAS data recovery are the same as those used for the
regular hard drive recovery meaning that almost all data recovery software can recover data from a DAS unit until
it operates as a whole.
Network Attached Storage
Network Attached Storage (NAS) is a device connected to a PC via network.
Such devices provide access to data at the file level rather than at the sector level.
NAS executes requests like "give me this piece of that file".
A NAS has its own filesystem the type of which is set once the NAS is configured and doesn't depend on the PC
the NAS operates with.
Since a NAS does not provide a direct access to its sectors, no data recovery software can work with it.
To recover data from a NAS, you need to disassemble the NAS, pull the disks out and connect them to a PC directly.
You have to do this even if you need to undelete just a couple of files.
Sometimes NASes are used for storing iSCSI files.
This seemingly violates the rule that the direct access to the sectors is impossible.
In fact, it's not. Actually, iSCSI provides another type of access to a particular file which is stored on
a NAS filesystem.