Jonathan's blog

I recently (mid October) moved my home server into my loft, as its constant noise under my desk was getting on my nerves.

However I found that with a large area of roof exposed to the sun (even the weak Autumn sun), and practically no ventilation the ambient temperature fluctuates enormously.

In October when it was a little warmer and a little sunnier, the temperature would drop almost as low at 10°C and almost as high as 30°C. An ambient temperature of over 25°C seems to drive my disk temperatures up to over 50°C. This constantly changing temperature with high and low extremes is a sure-fire way to break hard disks.

After Week 42, I opened the loft trapdoor, which went a long way to keeping the temperature more constant. Unfortunately it also makes the flat rather cold.

Now it’s much colder outdoors, I’ve closed the trapdoor again and the loft temperature seems pleasantly cool and reasonably constant. Today the temperature up there is a steady 13°C, although the sun hardly shone. That’s cooler than your average air-conditioned data centre – and all free thanks to the crappy British weather

Oh, and the 6 disks are now all between 25°C and 30°C.

• I’m measuring and graphing this using a TEMPer USB thermometer, using Nagios monitoring software with my own plugin and PNP4Nagios to draw the graphs.
• The “outage” between weeks 43 and 44 was caused by the shift from BST to GMT, apparently. I didn’t notice for a while, but restarting Nagios fixed it

Promise NS4300N

I decided to buy a NAS and remove the disks from my home server.

I didn’t want to spend too much money, since this was one of those non-essential projects. But equally, I didn’t want to spend too little and get something that would break and destroy all my data with it. Eventually I decided upon a Promise SmartStor NS4300N.

Features

It had all the features I wanted, including:

• SMB/CIFS for Windows clients
• NFS for Linux clients
• RAID5
• Gigabit Ethernet with Jumbo Frames

First impressions

So how did it shape up?

The build quality was relatively poor. It’s made from thin plastic and feels flimsy. The disk caddies are incredibly flimsy and flexible, and I felt nervous even handling them; but this didn’t matter because I planned to assemble it and leave it alone.

It wasn’t exactly quiet either. There is an 80mm fan for the disks and a 40mm fan for the internal PSU. The 80mm fan only spins when the disks are hot but it is very noisy when it does so. The 40mm fan is constant but not so loud. And of course there’s the sound of four hard disks, which varies depending on make and model. Overall, it’s probably quieter than a standard computer, but you wouldn’t want to sleep with it in your bedroom.

It’s not a problem for me because I’m putting it in the loft.

Setting it up

The initial setup wasn’t as straightforward as I thought it could (should?) have been, especially for beginners. But it wasn’t really much trouble to set up a RAID5 array with 4 x 500GB disks and format it, for a total of 1.4TB.

More confusing, perhaps, was the selection of different protocols and the layout for setting up users, shares and permissions.

I wanted to set up two shares, public and private and set public to be world-readable (for my media centre) and private to be accessible only by me. If you create these accounts on the NAS, it’s simple enough to tick the boxes and set the desired permissions on Windows (SMB/CIFS) shares.

But NFS was a different kettle of fish. No user-level permissions are available on the NAS for NFS, and the only control you get is a list of allowed IP addresses. By default the NAS says it allows *.*.*.* but I found that this didn’t let anyone in. Adding real IP addresses to the list worked.

However, I found that when you have data shared both as NFS and SMB/CIFS, the permissions go out of the window and are not respected at all. An unauthenticated guest user was able to read and delete files from my private share.

Performance

Performance was far worse than I had expected.

With the NAS mounted on my PC via NFS, it would only manage 4.8MB/s sustained write rate, and 13.5MB/s sustained read rate. That’s significantly worse than the sustained 30MB/s I used to get with the same disks in the server, as a Linux software RAID array. On top of that, writing at this speed tied up my computer’s quad-core CPU 100% with IOWait.

With the NAS mounted on the same PC via SMB, it was able to write sustained at 9.2MB/s.

This is really quite poor, given that the same set of disks when connected directly into the server with SATA could write at some 35MB/s.

It depends on your usage though – if you simply want to play music and videos from the NAS then 10MB/s is fine, even for high definition. However I use mine for large backups and I don’t want to wait almost ten times longer for the backups to complete.

Summary

• If you already have a NAS or storage server that you are happy with, don’t buy this.
• If you want to use NFS, don’t buy this.
• If you care about high performance, don’t buy this.
• If you want a reasonably-priced solution for backups or sharing media between computers, buy this. I reckon it would be fine to shove in a cupboard and simply drag your movies onto from your computer, so you could watch them on your media centre.

However, it didn’t cut the mustard with me, so I sent it back. I’ve now returned to my original system with the four disks hosted in the server. It’s fast and the permissions work fine – the downside is that I have to keep a large, noisy ATX tower case and can’t switch to an Intel Atom solution

My requirements

When I built this computer back in January, I had carefully considered the RAID storage configuration. My requirements were basically:

• Must dual boot Fedora and some flavour of Windows (unfortunately)
• Fedora must have a redundant /home partition, as it holds my most important data
• Windows must have a fast Media (aka /home) partition for my audio work
• Would also be nice to have redundant OS partitions

The initial plan

So I decided to buy a pair of identical 320GB disks for the OS, a set of three 640GB disks for my media. My new motherboard had 4 SATA ports on an ICH10R controller, and 2 SATA ports on some other SATA controller.

It seemed best to set up a fakeraid RAID5 array across the 3 media disks in the ICH10R controller, and to let the OSs do their own thing on the 2 OS disks.

I split both of the OS disks in half to allow Linux software RAID1 (mirroring) across both of its RAID partitions, which would be mounted as /. The two partitions showed up to Windows as C: and D:. It is not possible to use Windows software RAID (aka Dynamic Disks) on a Windows boot partition so I installed Windows on C: and used D: for Program Files.

I created a RAID5 array across the 3 disks using the ICH10R RAID BIOS. Booting into Windows, it was immediately spotted so I cut the device in half and created drive J: for my media. Sorted – it was fast and worked nicely.

No such luck with Fedora 10 (the latest relkease at the time I built this PC). Anaconda, the Fedora installer, was not able to see the RAID partition – it only saw the three separate disks. Try as I might, I could not get round this. Kind of a showstopper.

Onto plan B

I figured that I could avoid using the ICH10R fakeraid by keeping the disks as 3 separate disks, cutting each in half and using three halves for Linux software RAID, and 3 halves for Windows Dynamic Disks. No such luck – Windows is only able to use a whole disk as a Dynamic Disk, and wasn’t able to share it with Linux. Bugger.

What I ended up with

Given that Windows and Linux cannot share a RAID array, whether it be software or pseudo-hardware, my only choice was to somehow divide up the disks.

The two OS disks were fine as they were; Windows was not using RAID but rather a more manual approach to having two disks (OS on C: and Program Files on D:).

Eventually I decided to give Windows two of the media disks and use them in a RAID0 (striped) Dynamic Disk for performance. This still gives approximately the performance of a 3-disk RAID5 array, but without the redunancy. I get around this by not keeping anything permanently on the RAID0 array. It is only used as a cache/buffer during audio work, and the audio files are primarily stored on my server via the network.

This left just a single disk for Fedora’s /home partition. It doesn’t tick the box of having redunandcy, but thanks to my hourly backup script this is less essential.

This diagram shows my current sub-optimal setup. Click for a bigger version. Windows partitions are in red and Linux in blue.

My partition setup

The future

Since setting up this PC, I happened across a blog post that seems to be the answer to my prayers. It’s a bit hacky, but it’s the only documented way I have seen of getting a dual-boot system to share an ICH10R array.

Next time I can be bothered to reinstall both OSs, I will write about it here.