how to let aufs use more than 127 layers? or an alternative to it

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                          I came to the conclusion that aufs is limited to 127 layers based on tests.  

**(prepare)**

    mkdir write joined {1..400}
    for((i=1;i$i/$i.txt;done #for checks

**using a single mount, the limit is 84 layers (numbereds + the write one).**

The folder name doesn't change the 84 limit (so each could be bigger ex. "layer-72", therefore not a string size limitation).

    sudo mount -v -t aufs \
      -o "sync,br=write:1:2:3:4:5:6:7:8:9:10:11:12:13:14:15:16:17:18:19:20:21:22:23:24:25:26:27:28:29:30:31:32:33:34:35:36:37:38:39:40:41:42:43:44:45:46:47:48:49:50:51:52:53:54:55:56:57:58:59:60:61:62:63:64:65:66:67:68:69:70:71:72:73:74:75:76:77:78:79:80:81:82:83:84" \
      "none" "joined";echo $?

The above will fail, unless you remove ":84" from the end.

**Using remount, it can go up to 127 layers (numbereds + the write one)**

    sudo mount -v -t aufs -o "sync,br=write" "none" "joined";echo $?
    for((i=1;i<=400;i++));do 
      echo "try $i";
      if ! "sudo" "mount" -v "-o" "remount,append:$i" "joined";then
        break; # it stops with error "No space left on device", but is not related to free bytes on storage!
      fi;
      ls -l joined/$i.txt;
    done

**research**

I am trying to use mount.aufs just to see readable error messages, as mount -v is not helping.  

Is there documentation specifying how to translate mount parameters to mount.aufs?

I am still trying to find mount.aufs source code too; that could help my understanding of what parameters it accepts.

**Alternative acceptable answer**

Is aufs patchable (as apparently 127 is a hard-coded limit)? Is it worth the effort/mess, or more than 127 may cause performance issues as suggested on comments?

Could an alternative folders merger provide more than 127 layers? If so, which one? Here a list I found: overlayfs unionfs mhddfs mergerfs docker. What commands I should use based on the test case I provided above? aufs is quite clear and simple to use and understand, and that was the main reason I chose it.

PS.: I am using this now: https://unix.stackexchange.com/questions/704168/how-to-make-mergerfs-behave-like-i-did-aufs-behave-only-write-everything-new-or/730165#730165 
                        

Asked by Aquarius Power (4537 rep)

Nov 12, 2017, 12:57 PM
Last activity: Dec 31, 2022, 04:20 PM

how to let aufs use more than 127 layers? or an alternative to it

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