Best disk setup with different drives

  • Hi guys,


    I'm currently using a Synology NAS with 4x 2TB WD Red drives and want to switch over to OMV. I will probably keep my existing drives, maybe add another one and I'm trying to figure out, what the best disk configuration might look like. A solution with UnionFS + SnapRAID seems to be the best right now.


    Idea 1: 4x 2TB + 1x 8TB drive in my new NAS. The 2TB are all data drives (UnionFS pool), the 8TB is for parity.
    Question: How much of the parity drive could be used for data and would there also be any redundancy, in case the drive fails?


    Idea 2: Idea 1: 3x 2TB + 1x 8TB drive in my new NAS. The 2TB are all data drives (UnionFS pool), the 8TB is for parity. One 2TB disk used externally to backup the most important data independently.
    Question: How much of the parity drive could be used for data and would there also be any redundancy, in case the drive fails?


    A general question I'm asking myself is: How big is the parity part of a file. Eg a file is 10GB, how much space will it use on the parity disk?


    I'm open to all suggestions.


    Thank you!

    • Offizieller Beitrag

    is it even possible, to use one physical hard drive as DATA and PARITY disk at the same time?

    I could be wrong as my experience with Snapraid is pretty limited, but I don't think so. If I'm not mistaken, the parity drive also does not have redundancy... but it's been quite some time since I messed with Snapraid.


    If you're gonna use Snapraid and Unionfs (which I'm really not a huge fan of), I personally like Option 2.. as it gives you an external backup of important data.. but I would nix the idea of using the 8tb for Parity and Data.

  • I could be wrong as my experience with Snapraid is pretty limited, but I don't think so. If I'm not mistaken, the parity drive also does not have redundancy... but it's been quite some time since I messed with Snapraid.
    If you're gonna use Snapraid and Unionfs (which I'm really not a huge fan of), I personally like Option 2.. as it gives you an external backup of important data.. but I would nix the idea of using the 8tb for Parity and Data.

    Thanks. Yes, if I can't use it as both, I won't need 8TB. Maybe a smaller one 3-4TB... Whats your issue with UnionFS? Any other recommendations?

    • Offizieller Beitrag

    Mainly because i use a lot of Dockers and there's an issue with docker containers starting properly on a merged filesystem.


    There's a bunch of threads here on the issue including some folks who wrote some scripts to try and correct the problem. I didn't bother going that far with it.

  • oh, that doesn't sound too good... but is it just the appdata folder that makes problems or also the media files (if the docker would be sonarr or radarr)? do you know any better solution than UnionFS and SnapRAID?

    • Offizieller Beitrag

    A solution with UnionFS + SnapRAID seems to be the best right now.

    The issues with Dockers and UnionFS, that @KM0201 , mentioned is that both function in a manner similar to OverlayFS.


    They distribute files and folders, among several folders, then merge them back together as if they're all housed together in one folder or, in the case of a VM, a single file that acts as a virtual drive. The net result is that, files that appear to be in one location have, in reality, been exploded over several locations and, potentially, several drives.


    You can use UnionFS+SNAPRAID with Dockers and VM's, but a few rules of thumb should be observed to prevent problems.


    1. Use a simple file system, as the base, for UnionFS and SNAPRAID. EXT4 or XFS.
    2. In UnionFS (really it's mergerfs), use the default storage policy, "Existing Path, most free space."
    3. Do not use a single folder ( Server_Folders for example) at the root of the mergerfs mount point, and install your shares inside it. Your individual shared folders should be at the root of the mergerfs mount point.
    4. When you populate the mergerfs mount point with data, start with the largest shared folder first. Generally this will a videos share, and proceed from the largest to smallest shared folder. (Don't be surprised if one drive has the share "videos" on it, and the other drives contain all of the remainder of your shares.
    5. Setup separate shares for Docker storage (Dockers) and a share for storing VM's (VMs). With default storage policy, "Existing Path, Most Free Space", mergerfs will create these folders/shares on one drive, and not distribute them.


    Ideally, to prevent unanticipated problems, a dedicated (2TB) drive could be used exclusively for Dockers and VM's. SNAPRAID can protect it, even if it's outside of a merged UnionFS drive. Simply add the drive, to SNAPRAID, as a data drive.


    is it even possible, to use one physical hard drive as DATA and PARITY disk at the same time?

    You could do this (using Gparted to setup block partitions on the drive). But, given the way SNAPRAID works, you couldn't protect the data partition(s) of the 8TB drive. If the 8TB drive fails, the parity partition dies with it, so the ability to restore the 8TB drive or it's individual data partitions dies as well. As a consequence, it wouldn't be possible to protect the data partition(s) on the 8TB drive. (But you could use the partition for non-critical, "throw away", storage.)


    For a SNAPRAID parity drive, all you need is a drive that's physically identical to, or slightly larger, than the drives to be protected. In your case that's a 2TB drive. I'd buy another 2TB drive, to serve as a SNAPRAID parity drive and use the 8TB drive, with another host, for backup. (A full second copy of all your data, on another host, is ideal.)

  • Actually a versionized copy on a second host would be way better to protect from accidentaly removing data or simply corrupted data. Does not help to have a backup when the copy gets overwritten every time, including the corruption.

  • Wow, thanks for all the tips and feedback. I'm also gonna have a SSD in my NAS for VM's. I guess I could also store the Appdata folder on it. With a daily backup of the folder, I should be good to go. Ideally I'm able to sell my Synology NAS including the 2TB disks, but so far I have no luck... I didn't start buying anything yet, because a few things are still unclear about existing hardware I can use... I will definitely ask for feedback, after I have finalized the things I'm gonna buy...


    A regular RAID would always be the easiest option, but I really like the power and noise saving advantage I get from SnapRAID :)

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