Disk usage not accounting for external storage

SYSTEM INFORMATION
OS type and version Debian 10
Webmin version Latest Free

Hello,

I have an external drive hooked up to the server under the /raid directory. The storage is accessible from within the system but the Disk Usage section on the dashboard doesn’t show that.
This is how it’s shown on the dashboard:


This is the output of the df -h command:

➜  ~ sudo df -h
Filesystem      Size  Used Avail Use% Mounted on
udev             32G     0   32G   0% /dev
tmpfs           6.3G  690M  5.7G  11% /run
/dev/sda2       2.1T  824G  1.2T  42% /
tmpfs            32G   52K   32G   1% /dev/shm
tmpfs           5.0M     0  5.0M   0% /run/lock
tmpfs           6.3G     0  6.3G   0% /run/user/1000
/dev/sdb2       1.9T  696G  1.2T  38% /raid
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/14b383d4b78b3514d907454b3fef95bdf3ecd08fa2bd9bdf59fa115bed877fe7/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/5837a7ef31d135ffe20ea4d65b4fc206fc4f42d0f0e4ab4fb56ec81156c0f150/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/457e09dc4210710eeba7735c9f1546124c18224e400e45c3a693215983cb9a15/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/14df81edb72894db5af5ed2887ca11ca240df8636239b4aa815e2a4af68344d0/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/98882dcfc5b0dc980d75db0402a073f6d61cca60526f212d6f015f10a2b7dce8/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/f5310614568df2e9f23f76189c82575c997fcc0bf081eabda0252d4fa1092a5f/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/ca2351db7e1dfd27e4ec88de3ff8407cc4fb7fa0ea8ef7450fa36934699b0e1a/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/420ca1a2bce8b47799ba99aeede0d03a4769dcd0bd90264eb0e022078f86f07f/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/be8a4020032a8090527b17dd1acea4b14d4d1218c47a81c0d2870793fe4dc6e9/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/4f53bdd34163fa649d981d0fe9a298c549510983a40160d9e6a85c1e81273781/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/f786a1d3ffad962dbf4535b011019a2b51fc28a86d7ff646f6be8a3203229462/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/374476f90485b48df2c421d86b429273de749029e4003c3d7dcf087f2b9be281/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/51e900eb949c9ba999bbfd61504f0deb1bc756bf331ddc9884420cb1015b3278/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/fc6d19d96eb38a176580b4d16d0b270c8eedfc8ea7c0650cdc4fc83909aa1cc2/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/9ba1ba18551cbdb390e2405863e42f662c236d125ec9774b92f97c661938683e/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/67acd07790eedd1174307d49914e6fb0818455b572d551dd8d206594fac3d177/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/07559770a2112cee12f85720fdeefcda096022888b9aa865bb22ab072f4f32aa/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/75ca0e6c79577e9f115a52b0c878bfc039d90fcc0f1d763b9980ca1410e1bac1/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/6647efb9590fe941e5a69938ff16687e50159caa8418af357901789c57160e6a/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/b0ef0cab8795bc8cb57271c5e233e3d33aec1fe687b0fd795a1a055675807e97/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/df158311a02aeca2fe325f8ca30f8f6b5be2f31a0e8eafcc790064adcb35f74c/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/59ae7eeb8cc54f740f41b3bd4c9e9f8fef6770f0922b2e2060b58242e111f8dc/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/4b50ec4b2fa4d04bd363f5ec0d4879cb3711f445d16d75f5cd8ab34ccea965fc/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/2ffb84bf543c722f6ef8191a410572e4008b383fc68064b4f47255019730bff6/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/7a77486fa1a25b6d1ebf70c139d058b760e95289f77659f08380894d22ec59c6/merged
overlay         2.1T  824G  1.2T  42% /var/lib/docker/overlay2/0a2bbfaa284f7e47cb20532b77b9a4d6673bcff77ec688cce16c6d3cc87fbe9c/merged                                                         /0.0s

Notice how both storage devices (/dev/sda2 and /dev/sdb2) are properly shown in the output of the command. The /dev/sdb2 disk also shows correctly under the Webmin → System → Disk and Network Filesystems (couldn’t post more pictures because of new user limitations)