OpenMediaVault – Annoying mdadm e-mails after a rebuild

My homebrew NAS running OpenMediaVault (based on Debian) started writing to me recently. I’d had a disk failure and replaced the disk in the RAID set with another one. Everything rebuilt properly, but then this mdadm chap started sending me messages daily.

"This is an automatically generated mail message from mdadm
 running on openmediavault
A SparesMissing event had been detected on md device /dev/md0.
Faithfully yours, etc.
P.S. The /proc/mdstat file currently contains the following:
Personalities : [raid6] [raid5] [raid4] 
 md0 : active raid6 sdi[0] sda[8] sdb[6] sdc[5] sdd[4] sde[3] sdf[2] sdh[1]
 11720297472 blocks super 1.2 level 6, 512k chunk, algorithm 2 [8/8] [UUUUUUUU]
unused devices: <none>"

Which was nice of it to get in touch. But I’d never had spares configured on this md device. The fix is simple, and is outlined here and here. In short, you’ll want to edit /etc/mdadm/mdadm.conf and changes spares=1 to spares=0. This is assuming you don’t want spares configured and are relying on parity for resilience. If you do want spares configured then it’s probably best you look into the problem a little more.

OpenMediaVault – A few notes

Following on from my brief look at FreeNAS here, I thought I’d do a quick article on OpenMediaVault as well. While it isn’t quite as mature as FreeNAS, it is based on Debian. I’ve had a soft spot for Debian ever since I was able to get it running on a DECpc AXP 150 I had lying about many moons ago. The Jensen is no longer with us, but the fond memories remain. Anyway …

Firstly, you can download OpenMediaVault here. It’s recommended that you install it on a hard drive (ideally in a RAID 1 configuration) rather than on USB or SD cards. Theoretically you could put it on a stick and redirect the more frequently written stuff to a RAM disk if you really didn’t want to give up the SATA ports on your board. I decided to use an SSD I had laying about as I couldn’t be bothered with more workarounds and “tweaks”. You can follow this guide to setup some semi-automated backup of the configuration.

Secondly, here’s a list of the hardware I used for this build:

  • Mainboard – ASRock N3700-ITX
  • CPU – Intel Quad-Core Pentium Processor N3700 (on-board)
  • RAM – 2 * Kingston 8GB 1600MHz DDR3 Non-ECC CL11 SODIMM
  • HDDs – 1 * SSD, 8 * Seagate Constellation ES 2TB drives
  • SATA Controller PCIe x1 4-port SATA III controller (non-RAID), using a Marvell 88SE9215 chipset
  • IO Crest Mini PCIe 2-port SATA III controller (RAID capable), using a Syba (?) chipset
  • Case – Fractal Design Node 804
  • PSU – Silverstone Strider Essential 400W


You’ll notice the lack of ECC RAM, and the board is limited in SATA ports, hence the requirement for a single-lane, 4-port SATA card. I’m really not the best at choosing the right hardware for the job. The case is nice and roomy, but there’s no hot-swap for the disks. A better choice would have been a workstation-class board with support for ECC RAM, a decent CPU and a bunch of SATA ports in a micro-ATX form-factor. I mean, it works, but it could have been better. I’d like to think it’s because the market is a bit more limited in Australia, but it’s more because I’m not very good at this stuff.

Thirdly, if you do end up with the ASRock board, you’ll need to make a change to your grub configuration so that the board will boot headless. To do this, ssh or console onto the machine and edit /etc/default/grub. Uncomment GRUB_TERMINAL=console (by removing the #). You’ll then need to run update-grub and you should be right to boot the machine without a monitor connected.

Finally, the OMV experience has been pretty good thus far. None of these roll-your-own options are as pretty as their QNAP or Synology brethren from a UX perspective, but they do the job in a functional, if somewhat sparse fashion. That said, having been a QNAP user for a about 7 years now, I remember that it wasn’t always the eye candy that it is nowadays. Also of note, OMV has a pretty reasonable plugin ecosystem you can leverage, with Plex and a bunch of extras being fairly simple to install and configure. I’m looking forward to running this thing through its paces and posting the performance and useability results.