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Network Attached Storage

Posted by coldtobi | 14 Oct, 2007, 17:39

Last week, at a local groceries discounter, they has an NAS on sale, but were already out of stock at the time I was there.

To be more precise, it was actually an NDAS (<--warning: marketing speech. Read their FAQs for a bigger picture.), so afterall I am not mad that I was too late.

As I was not familiar with N(D)AS, I did some research, and found, that NDAS has some properties which I don't think they are appropiate for a NAS. Others would call this "just cost-optimized".

NDAS uses some proprietary protocol which is a kind of direct-access (thus the name) to the attached (physical) harddrive. So it is best described as a kind of "ATA over Ethernet".  

Proprietary solutions requires users proprietary drivers to be installed. This is also the case with NDAS. This is not a big deal, as this is an one time thing. (for the score: It like the same as configuring a LAN. IMHO configuring a LAN is less stress than installing drivers. Ever made the "hopefully-this-time-it-gonna-install-experience?". I did. With some gfx-card driver....

Another plus-point for NDAS is that Ximedia release linux drivers, packed for several distributions. So it will work with linux, and the made also a NDAS How-To. But the driver is only for available for a limited set of kernel versions. For debian, it is only available for kernel-version 2.6.18_1_686. (but etch is currently at 2.6.18_4). So it won't work out-of-the box, however there is a "general" linux package available, which seems to contains the source needed to build the modules for any kernel. As I do not own a NDAS, I won't try this. ( Feedback is appreciated.)  On the other side, you are getting dependent on the manufactor, and a tainted kernel. (As you see, the are still at a very old kernel, which they built the drivers for. In the later kernels, there where some significant API change, and I'm auite unsure if it would compile with arecent 2.6.22 or later. Just for the record: My shiny AMD X2, a 64-bit processors is not supported, but I anyway use -x86 kernels for now.

("Plain" NAS do not need drivers at all.  So this is a tie in the comparison NDAS vs. NAS. )

Ethernet sound goods, but not everything using Ethernet does come with TCP/IP: NDAS is not using TCP/IP as transport layer, which could lead to problems if for example routing (differnet subnets) or WLAN is involved. As I use both at home, this alone is the k.o criteria for me. 

Direct access on the media requires the drivers or the operating system to user their own file system drivers. This open the freedom which file system to use on the (physical) harddrive, but on the other side, file systems are usually not designed for multiple write accesses from different computers at the same time.

NTFS seems to cope with that. (But I don't know if this is a real NTFS feature or driver feature. I think NTFS.) However, as I have an mixed network at home (Linux & Windows), NTFS would not be an option. The open source NTFS driver is still missing some essential features. (Well, reverse engineering a filesystem is a hard job.

As the file systems known to Windows are limited, the only other practicable solution would be an FAT32. But here, NDAS sucks: All computers -- except one -- has to mount the volume read only. Yes, READ ONLY. That's not the purpose of Network Attached Storage.  

The recommend maximum of 16 concurrent accesses to the media, which are recommended not to exceed should be not a problem, if one computer is accounted as one access. (The technical maximum ought to be 64.) 

Okay, NDAS is pretty fast. Usually "real" NAS won't perform that fast (NDAS claims to reach around 20 MB/sec, where the (affordable) NAS Solutions I checked already will not go beyond 10 MB/s), but for my personal targeted use, I think, they are outweighted by the cons. 

My Conclusion

NDAS:

Pro:

  • Linux-Supported by Company,
  • Cheap,
  • Fast
  • Flexible at filesystem. 
  • No network configuration needed

 Neutral:

  • recommend 16-users-max 

Con:

  • Needs propriety drivers instaled on every computer
  • taints kernel, probably needs to mess around building drivers for own kernel.
  • No 64-bitter
  • Needs Cluster-File-System for multiple write access. (Hardly suitable for a Linux/Windows network.)
  • WLAN/Network topology issues, as not running on TCP/IP. Can't use as global share. 

Additionally, on some NAS systems you can run your own applications. I love that. But thats a geeks-pro for NAS. 

I think, I will go for an NAS, even if the price for NDAS is, well, better. I'll prepare a comparison about some NAS solutions out there, below €200.

 

Links:

 http://www.linux-user.de/ausgabe/2006/10/076-datastation/index.html

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