Adam Retter

In deciding to build my own NAS, after having identified my requirements in Part 1, I set about searching for the perfect hardware and software combination...

There are plenty of open source operating systems available that offer multiple options for reliable storage, including both hardware and software supported RAID. To avoid getting into the situation of outdated/unsupported hardware again, I have decided not to use any sort of hardware assisted RAID, instead I will use the software RAID support provided by the operating system itself.

Many of these operating systems support a vast array of system hardware, however I did not want to just reuse a standard PC/Server because of its large power requirements and physical size when compared to commercial NAS systems aimed at the SMB (Small and Medium Business) Market.

Software

Linux, FreeBSD and OpenBSD all offer options for software RAID. There are also a number of distributions specifically designed for NAS appliances such as OpenFiler (based on Linux) and FreeNAS (based on FreeBSD), however I have settled on OpenSolaris because of ZFS and its RAIDZ feature. Also worthy of a mention is the very interesting and well suited looking NexentaStor (based on OpenSolaris), but the added goodness is not open source, so I will consider it no further.

A few reasons why I chose OpenSolaris and ZFS -

• OpenSolaris is based on Solaris (it feels solid, just like Solaris)
• OpenSolaris has CIFS and NFS support built in
• ZFS RAIDZ and RAIDZ2 provide better than RAID functionality
• ZFS has 256 bit checksumming and self healing
• ZFS does not suffer from the RAID-5 write hole
• ZFS snapshots

Looking at ZFS and the reliability of disk failures I decided to go for a RAIDZ2 approach, which requires at least 4 disks.
RAIDZ2 is an advancement of the traditional RAID-6. It writes a double-parity and parity is distributed across the disks. In this configuration approximately 50% of your total disk space is available for file storage and the other 50% is used for parity information. In RAIDZ2 with four disks, continuous operation is ensured even with the failure of two of the disks.

Simon Breden has written some excellent blog entries on building a home fileserver using ZFS, he has informed my decisions and I think perhaps he explains the salient points more eloquently. A article of Simon's on the advantages of using ZFS is here

Hardware

My first and by far hardest task was finding a suitable chassis for my DIY NAS. I wanted it to hold at least four disks for storage, and one disk for its operating system – so a total of 5 disks... and it needed to be physically small, this is my home not a data-center.

Originally after much searching, I found the Norco NS-520, which looked absolutely perfect; it supported 6 disks, came with a Mini-ITX motherboard, Celeron-M processor, 512MB RAM, 180W PSU and was physically small (277x187x230mm). Unfortunately the cheapest option was shipping it directly from the manufacturers in Shenzhen, China at $687 =~ £464.82. The cost seemed high (and would of been higher after import duty and VAT) and the maximum power consumption was more than I had hoped for.

The only other NAS chassis that I eventually found was the Chenbro ES34069, again it ticked all the boxes; it supported 5 disks, accepted a Mini-ITX motherboard, had a small 120W PSU and was physically small (260x140x260mm). It was also available from a UK reseller for £205.85 inc.VAT. Cheaper than the Norco (even after adding a motherboard, CPU and RAM) and the maximum power consumption was lower :-)

For the Chenbro chassis I needed to source my own Mini-ITX motherboard. The main requirement was that it support at least 4 SATA disks for my storage and an additional IDE/SATA disk for the operating system and have a low power consumption. Finding a motherboard with a low-power CPU and at least 4 SATA ports turned out to be a tough task, I found only two –

• VIA EPIA SN 18000 EG – VIA 1.8GHz C7 32bit CPU / 26W - £178.25 from mini-itx.com (inc. VAT)
• MSI IM-945GC – Intel Atom N330 1.6GHz Dual Core 64bit CPU / 24.33W Max - $169.00 from orbitmicro.com (£191.13 after currency exchange, import VAT and handling charges)

I chose MSI's Intel Atom board as it offered considerably more processing power at lower power consumption, it is also 64 bit unlike the VIA - there are rumoured problems with ZFS on 32 bit systems.

I would also like to take a moment to congratulate MSI on their excellent pre-sales technical support, a quick call to their UK office and within a day their Taiwan office had emailed me the power consumption specifications for the motherboard :-)

The complete bill of materials and estimated power consumption follows. The remaining items were chosen for their suitability with the chasis and motherboard and/or for their low power consumption.

Read more in Part 3 - Building my DIY NAS.

tags: NASRAIDZOpenSolarisChenbroMSI

Thanks for the quick reply, Adam.  This is the best hint I found on the issue so far: http://www.mail-archive.com/[email protected]/msg24383.html.  I suppose if Intel isn't putting ECC on the i7, there's not reason to expect they'll put it on the Atom.  Maybe ARM or another competitor will do it though.
                                        
                                        How has your ZFS box been performing by the way?  I'm still interested in the idea of a low power ZFS box.

Hi Adam, your setup looks very nice.  It's much neater and offers better performance than hooking up USB drives to a nettop, which was my initial plan.
                        
                        Do you happen to know if there are any Atom motherboards coming out in the future that will support ECC though?  That would be the icing on the cake in addition to the 4 SATA ports.

                Fred, the power consumption listed for the motheboard is from the MSI motherboard manual itself.
                The maximum power consumption is based on a heavy Windows benchmark - they dont provide much detail, but I think it must include the processor and presumably therefore some sort of RAM.

Hi Adam, 
                
                this is truely interesting, as I am about to do the same as you.... always on server.... but I run mythbackend as an additonal process as well as typical Nas like functionality and squid.
                
                Before I spend any money I have been also looking at a different approach Foxconn G31MG-S + e7200 (31 Watt at idle)... seems amazing.
                
                Can I ask ..... does your Power consumption figures include the watts need for the N330 (i.e. + 8Watts)?  Also do we need to add some for the 2GB DDR?
                
                Thanks for a truly enlightening blog.
                
                Fred.
                
        

Luke,
                                
                                Sorry, I am not quite sure what Intel are planning in the future with regards ECC, I could not find any official roadmap for Atom. The unofficial roadmaps that I found did not mention ECC.

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