I am just wondering how to compare the various terabyte RAID storage systems and what features are most important? The cost differences between the reviewed system and the Buffalo are significant I believe.
The easiest way to break a comparison down is into four components:
1/ The discs
2/ The front end processor
3/ The software
4/ Power and interfaces
The first item, discs, is an obvious cost differentiator. The larger the capacity of the NAS, the faster the discs (spindle speed, read/write times and sustained transfer rate), and the higher the quality then the more expensive and better performing the NAS solution.
The second item is the front end processor. The easiest way to visualise this is to consider the NAS as a dedicated computer with a bunch of discs attached which you connect to the network, though instead of a windows/mac/linux machine you have dedicated processing hardware with custom software loaded. The more powerful this front end processor the more user can be connected to the NAS, the faster the aggregate throughput of data and the more complex features that can be supported. More power, as with computers, equals more cost. Also devices may choose to adopt a software based RAID controller or a hardware solution which will affect performance and cost. In addition the NAS may include such items as caching (in addition to the 8Mbytes that may be on an individual disc) to speed up delivery of frequently accessed files; and may also include non volatile RAM to hold journaling data and to provide greater security of data in the event of a power failure. Both of these items will significantly increase cost.
The third item, software, covers a wide range of options and provides the most visibile differentiation between NAS devices. At a basic level the NAS needs to support various network file systems (SMB/CIFS and NFS) and some form of tool for partioning and maintaing volumes on the disc. Cheap NAS probably use a common disc filing system (FAT32, or one of the linux/unix equivalents), more expensive NAS use custom file systems which deliver better performance. Beyond that you can look at security and whether password can be applied to volumes (a password shared between all users so that they all have equal access to the data on a particular partition), and individual passwords (allowing finer grained security of files). Additional software may be included to allow snapshots to be created, perform accelerated reconstruction of RAID arrays in the event of failure, remote access, remote management, automated backup to other devices...the list goes on and depends how deeply you want to get into such devices and how sophisticated your requirements are.
The final item is power and interfaces. The worst situation is that the power fails whilst you are mid way through writing a file to disc. Whilst the NAS may not include a UPS you still need to make sure that the power supply is good enough quality that it will not burn out during the lifetime of the device (though this can be considered a low risk for reasonably priced systems). When attaching a UPS to the NAS there needs to be a communication between the two devices to ensure that in the event of mains power failure sufficient power is available to ensure that the NAS can shut down gracefully (allowing users to finish writing files and flush all cashed data to the discs) to ensure that there is no loss of data or disc corruption. In addition, you want to make sure that the NAS device can support all data interfaces that you may need: gigabit ethenet, USB in client mode - so that the NAS can be directly connected to your PC if you don't have a network, firewire, USB in server mode if you wish to connect additional discs (though probably not in a RAID configuration unless it is done in software).
At the end of the day the market for NAS devices is sufficiently competitive that you will end up with more perfomance the more money you pay. However, for the solo user there is probably benefit in going a little way up the cost curve (to get good throughput and build quality) but not so far that you are paying for the ability to connect 100s of users and very advanced software features.
In such a short post I have probably missed a bunch of stuff out, but it should give a flavour and a starting point for asking further questions.
