SnapRAID Split Parity Sync Script13 min read

SnapRAID v11 adds a sweet new feature, split parity. In the past, adding larger data disk always came with the issue of needing parity disks as large or larger than your data disks. For example, let’s say you add an array made up of (4) 4TB data disks and (1) 4TB parity disk. What if you want to buy one of those 6 or 8TB disks to use in your array? In the past, you could have either chosing to use the new larger disk as your new parity disk, or risk having part of your new disk not protected. With split parity, you could use the new 8TB disk as a data disk and then use (2) of your old 4TB disks, joined together as one complete set of parity (or, you could create parity in this scenario with (4) 2TB disks or even (8) 1TB disks). Pretty neat!

So, this would allow you going forward to add 6 or 8TB data disks and have all your data protected, without having to buy an extra one or two larger disks just to use on parity. Now that we’ve discussed split parity, how can we automate syncing like we did with my previous script? We can’t use that script as is because of the split parity files. So, I already had a modified version of my script, but when mtompkins presented his cleaned up version of my script, I thought I’d extend it for split parity and add a couple of extra functions. I present you now with the new split parity script (this version is setup for dual parity with 4 disks setup to complete split parity).

As a sidenote, I would love it if someone could provide a BASH method to read the snapraid.conf file and automatically build the array rather than having to manually set that up in the config. I fear with split parity, complex grepping may be over many user’s heads.

Here’s how I have the parity files setup from this example in my /etc/snapraid.conf file.



I love learning new things and trying out the latest technology.

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23 Responses

  1. woodensoul2k says:

    Hey Zack, it is still possible to use this script for just a standard dual parity setup? I plan on eventually using a split parity in the future but for now I was just wondering if I could use this new script after upgrading to Snapraid V11. I’m using your older script at the moment on Snapraid V10.

    • Zack Zack says:

      Great question. You can’t just drop this in and have it work, but with a very small modification, it should work fine. You would need to remove these lines.

      and replace them with something like this instead.

      or… if you have dual parity…

      You just need to adjust the names of the parity files that you have setup in your snapraid.conf file, and that should be it 🙂

  2. woodensoul2k says:

    Thanks for the easy explanation. Can’t wait to give it a go.

  3. Dulanic says:

    Is there any reason it unpauses the containers twice?

    • Zack Zack says:

      It only unpauses once, unless you have an error in your script so it doesn’t exit gracefully. Here’s the output of my run last night.

      • Dulanic says:

        FYI, it happened again. I don’t know what the heck is causing this… because I also get a “normal” email that shows it worked properly. The cronn process seems to be thinking it failed… and I guess it did, at least partially since it hit the 2nd restart and they fail.

        The 1st email fires off successfully and then the 2nd fires off when it failed immediately after when it tries to restart again. I think ti doesn’t send me off the fail email if I manually run it as it isn’t run automatically causing the cron failure email to fire off.

        • Dulanic says:

          OK sorry to spam your comments, but I did find that somehow the trap keeps being triggered but no idea how. I edited it to show “trap triggered” by replacing the function and it triggered at the end again. So I figured it looked like there is an issue /w the clean_desc function on my system, but I can’t tell why? So I tried replacing the trap /w…

          trap 'err_report $LINENO' ERR

          but now it isn’t triggering the trap. I did try changing to trap to a new function i had to echo trap triggered and it always did it at the end /w clean_desc . Since that worked for now I’ll keep it that way, and see if eventually it does trigger that so I can see where the line is that it errors on.

  4. Dulanic says:

    So odd, I did a notepad++ txt compare and the only 2 changes were the services and the the thresholds… yet I repasted it and it worked OK this time. Maybe a line break or something got messed up, no idea because even notepad++ couldn’t tell a difference. That was with a forced run, so we’ll see overnight I guess

  5. Dulanic says:

    So I have been using your script and mergerfs setup for a month now and twice I have run into an issue twice where it says something along the lines of…

    I have a feeling it is likely due to a file that mergerfs assigns to d4 that is either later moved or deleted between syncs. This is frustrating and the force empty sync takes forever. Is there any way around this?

    • Dulanic says:

      FYI what is the right way to post code? lol I keep trying things but can’t figure it out.

    • Zack Zack says:

      If you are running into needing to use –force-empty sync, you really need to check the files in question. In this case, this means that all of the files that were on /mnt/data/disk4 have been removed or have been deleted. If you haven’t completely removed all content from that disk, this means that something has went wrong. For example, a disk that didn’t mount, or a script that’s deleted all files, etc.

      To put this in perspective, I have never had to run –force-empty-sync unless, I have manually removed all files on a disk. I would do some more investigation.

      • Dulanic says:

        It looks like it was because of torrents soon after a disk got full… it would sync and then later on the files would be removed and boom that error showed up. What I did was add a DONOTDELETE.txt file to all of the drive to avoid the issue.

        • Zack Zack says:

          I would suggest handling all of your torrent downloading outside of SnapRAID. Or, just make a torrents folder for in process files, and then move the final, completed files to a location that SnapRAID is including. That way you don’t run the risk of a failed restore because of some missing files that were there during your last sync.

  6. oxzhor says:

    Hi Zack,

    I try to use your script on CentOS 7 and check all path this are the same like into ubuntu.
    But if i want to run the script i get the follow error:

    [root@media scripts]# sh line 121: syntax error near unexpected token >' line 121:
    exec > >(tee -ia “${TMP_OUTPUT}” ) 2>&1′

    I only modified the script so i can use dual parity, for the rest it is untouched.

    • Zack Zack says:

      Did you try the commented out method above to see if that works instead (obviously comment out the current exec line)?

  7. chad says:

    Zack –

    Thanks for your work on this, it’s been working very well for many months now! I have two related issues I need to ask you about. The background is that I’ve recently begun using Zoneminder for video surveillance. I have a single camera and keep recorded video for about 15 days. The way Zoneminder works is that it saves tens of thousands of files, sometimes hundreds of thousands of files per day. Then, after 15 days, those files are deleted in order to save space. This operation happens daily with just one camera. This would experience significant growth as cameras are added.

    You probably know where I’m going with this – your script sees these as massive changes to the system and tries to run the Snapraid operation but I’m receiving the following error:

    remove zoneminder/events/2/17/07/10/.1119
    remove zoneminder/events/2/17/07/10/.1120
    remove zoneminder/events/2/17/07/10/.1121
    remove zoneminder/events/2/17/07/10/.1122
    remove zoneminder/events/2/17/07/10/.1123

    613286 equal
    63606 added
    15725 removed
    1 updated
    0 moved
    0 copied
    0 restored
    There are differences!

    DIFF finished [Tue Jul 25 23:30:46 PDT 2017]
    **ERROR** – failed to get one or more count values. Unable to proceed.
    Exiting script. [Tue Jul 25 23:30:46 PDT 2017]

    As you can see, 63k+ files added, 15k+ files deleted but I’m not sure why the script is erroring out. Can you help with this? I’ve set my delete threshold to 10,000 but it’s still too low.

    The second question is there any way to exclude a folder from being included in the delete threshold count? With that method I can exclude my Zoneminder folder and avoid triggering the threshold nightly. Also since I have to increase the threshold, this opens opportunity for script to continue even if many files have been deleted in error.

    Again thanks for your great work!


    • Zack Zack says:

      Thank you for the kind words! The only way to figure out why it’s erroring is to re-create the script by hand (run a snapraid diff, and then run the grep’s that the script runs). I would think it’s due to the massive amount of adds/removes throwing my greps off.

      As a sidenote, I would strongly suggest you manage Zoneminder outside of SnapRAID (either moving them to a different setup (maybe a difference ZFS mirror array or exclude that path in SnapRAID). Rapidly changing files are not what SnapRAID is designed for at all. Rapidly changing filesystems can make recovery suffer/not work in the event of a disk failure.

      • chad says:

        Agreed. As I think about the use case of SnapRAID, it makes sense that it’s not designed for what I’m trying to do. Therefore I’m trying to exclude the folder but it’s not working and I think I’m not understanding the exclude option properly. In snapraid.conf I’m simply trying to ‘exclude /mnt/storage/zoneminder/’ but it’s not working neither is ‘exclude /mnt/storage/zoneminder/*”. Reading through the docs, it seems as though it doesn’t exclude recursively through all the subfolders (and Zoneminder has ALOT of them – one for each day AND timestamp). I saw a post where a user was able to exclude using ‘exclude /rootfolder/subfolder/*/*.jpg’ and ‘exclude /rootfolder/subfolder/*/*/*.jpg” and so on but that seems tedious.

        Any idea on how to handle this situation? My /mnt/storage is my main array and I want to keep my video storage on that.

        • Zack Zack says:

          Good question. The exclude is actually really easy. It is a relative path in the array. So, if your folder is at /mnt/storage/zoneminder, you would exclude that whole folder recursivly by adding just this one line to your snapraid.conf file.

  8. chad says:

    That did it, thanks!

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