Building a Linux Home Server

Building a home server turned out to be not so straightforward; here are my experiences, problems and solutions:

Motivation and Requirements

Hardware

Computer

I don’t need much computing power, so even the smallest machine should be sufficient – like e.g. a Raspberry Pi (and that’s what I used in the beginning). However, the I/O turned out to be a bottleneck, because the Raspberry Pi 1 had only USB 2.0 interfaces, which are way too slow for serious disk I/O. I needed SATA, which was not available in devices like the Raspberry Pi.

So I finally found the UP Squared which seemed to fit my needs best.

Storage Medium

Thus I decided to use 3.5" HDD drives; the WD Red series seemed to be a good candidate, being quiet and having a low power consumption.

RAID

A RAID should simply work; so the underlying technology should not matter. However, at first I had a simple USB RAID enclosure with two 2.5" HDDs; this had a few drawbacks: First, it was not possible to spin down the disks via software (as opposed to other USB disks), so they were running continuously; unsurprisingly, one of the disks failed after a few months. And second, rebuilding the RAID after replacing a disk seemed not to work, at least according to the blinking status LEDs. This was a big disappointment.

So I decided to use a software RAID; there, I have full control over the RAID and can also get S.M.A.R.T. information about the individual disks, and spin them down via hdparm. Thus, I needed a computer with multiple SATA ports.

SATA Controller

Because none of the small and energy efficient mainboards have multiple SATA ports, I needed an additional SATA controller. I decided to use a two-port SATA III Mini PCIe controller with ASMedia chipset, which is supported by Linux.

Disk Rack

Since a small computer does not have any hard disk bays, I needed an external enclosure with removable trays. However, only those for 2.5" disks have passive cooling; all enclosures for 3.5" disks have a noisy fan which is always running, even if the disks are spun down. But I found a disk rack from Thermaltek where the fan can be unplugged and the corresponding alarm be disabled. Since I am using only low power HDDs and since they are not running continuously, active cooling is not necessary.

Power Supply

Whereas highly integrated mainboards together with modern power management are very energy efficient, this is often not the case for power supply. Companies often sell high quality hardware together with cheap and inefficient mains adaptors; better quality exists mostly for powerful and thus expensive PCs, but not for embedded systems. But in order to keep the total power consumption low, an efficient mains adapter must be used.

Wifi Access Point

This turned out to be a major headache. There is a daemon, hostapd, which can turn many USB adaptors into access points. However, stability and software support were often a problem:

USB Audio Device

Since the UP Squared does not have an integrated sound device, I bought a simple USB sound card, Kotion S1 Pro.

IR Remote Control

I use FLIRC, a USB IR receiver which acts as a HID device. It can be used together with the hotkey daemon triggerhappy. I use it mainly for controlling MPD, i.e. setting the music volume, start/stop playing and skip to the previous/next song.

Software

Operating System

I decided to use Linux, since it is my preferred operating system, is well suited for servers, and has good hardware support.

File System

I wanted to have a copy-on-write file system:

I decided to use Btrfs, since it is included in the Linux kernel and offers all these features. Some people claim that it is not stable; I didn’t experience any issues, it turned out to be very reliable, but the documentation and maintenance tools need a lot of improvement. It does work well – but finding out what’s going on and what to do in case of problems takes a lot of time.

Software RAID

At the beginning, I used mdadm as software RAID, since it works well and reliably. But because it operates on cluster instead of filesystem level, rebuilding the RAID is very slow, and damaged files cannot be corrected since the filesystem checksum operate on the whole RAID.

So I switched later to Btrfs RAID, where checksum errors can be corrected with the second copy, and where only clusters that are actually used are duplicated to the second medium. Furthermore, disks do not need to have the same capacity, so one can switch to larger disks without leaving the additional part empty, and since Linux&nbsdp;5.5 also three or four copies are possible instead of just two. (But using btrfs replace one could already before exchange one of the disks without having only one data copy during the replacement.)

Daemons