RAID5 with external USB HDD

  • Hi,
    I have very little experience with OMV or storage (and just joined this forum). I had a RaspberryPi sitting around and a few external HDD so decided to build a small setup as an experiment.
    I've configured an RAID5 3-disk array and set up an SMB server for my LAN. I was just wondering what would happen if one of the drives is unplugged and plugged back in? Is the RAID damaged? Is the data corrupted? Does it affect one HDD or all 3? Does it make a difference whether it is reading/writing when this happens?

    Thanks in advance for your help

  • What do you suggest?

    Becoming familiar with concepts, benefits and technical limitations first :)

    RAID is ONLY about availability (a disk dies but the array continues to operate) it provides no means of data protection. Also RAID is about avoiding so called SPoF (single points of failure) and the internal LAN9514 hub chip inside your RPi is exactly this. Also performance with such a horribly slow platform like any RPi will suck as well as 'rebuild' times (if a disk failed and will be replaced a rebuild has to happen -- as long as the rebuild is running you have NO REDUNDANCY ANY MORE and if now the SPoF LAN9514 starts to fail or anything with cables/connectors goes wrong which is quite common with USB all your data has gone)

    Any RPi can already be considered worst platform possible for OMV, combining this with USB RAID is simply insane. Don't do this if you love your (valuable) data. If it's worthless then you don't need any redundancy anyway... it's really just a bad idea (USB RAID in general but combined with those lousy Raspberries it gets really just insane)

    Some better variants listed here: Which energy efficient ARM platform to choose? (but RAID is not advisable with any of them except maybe the Helios4 -- and before you start thinking about RAID/availability always take care about data protection first --> backup is the most important task to implement when it's about storage)

  • Thanks tkaiser, that insight was really valuable...
    However I did mess up. I put some data into my RAID5 array, the RPi rebooted and now the OMV doesn't show any RAID array anymore.
    I am trying to look for a solution for this - some way to recover those files in there - and never try anything like this ever again.

    Where would you suggest I begin? I could give you some details if you show me what commands I have to issue, or what screenshot I can take from the GUI ?

    Thank you in advance.

  • tkaiser

    I was able to solve it with the following

    root@raspberrypi:~# mdadm --assemble --scan
    mdadm: /dev/md0 has been started with 3 drives.

    However, lesson learned!! I think I'll go back to JBOD storage, and probably look for a more resilient alternative

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