For the first time I tried to create a secondary pool (not a cache) on Unraid.

The process is either stuck at formatting or mounting, depending on if I format & create the filesystem via console (stuck at mounting) or inside the Unraid GUI (formatting). The attached part of the syslog shows the error "emhttpd: error: mkmbr, 2307: Is a directory (21): open: /dev/" and "kernel: emhttpd[22405]: segfault at 628" consistently when I try to format either btrfs or zfs on my 2x20TB Exos.

 

I don't know if I am doing something wrong, but I want to use this pool as my media pool for movies and series - not as a cache.

My main pool is inside a TruenasVM and my array is only 500gb on 2 ssds for system data (iso's, docker images, selected VM images).
I wanted to use the btrfs (Raid1) pool for ease of use compared to my ZFS pool and because I don't want the RaidZ2 redundancy of my main pool. 

Any ideas what I am doing wrong or if this is a bug ? I was able to mount the formatted filesystem via console ... so my guess is this should work flawlessly inside the GUI ?

Thanks for any help. 

log1.txt log2.txt

I also forgot: I successfully ran a pre clear on both disks. They didn't indicate an error.

if terminal access is what you have type diagnostic need full daig to assist.

do you have something in the go file breaking something's?
stop array go into maintence mode and check disk for smart and file system checks.
you may need to edit the file system and set them to auto...

 

General troubleshooting:
 

Check for Common Configuration Issues

Ensure the Drives Are Healthy: Run a SMART test on your 2x20TB Exos drives to verify there are no hardware issues.

From the Unraid GUI: Go to Main > Disk > SMART Test.

From the console

smartctl -a /dev/sdX

Replace /dev/sdX with the correct drive identifier. lsblk...

 

 

Verify Disk Assignments: Confirm the 2x20TB drives are not already part of another pool or the Unraid array.

File System Choice: You’re attempting to use btrfs (RAID1) or zfs. If you switch between these formats frequently, remnants of previous filesystems can cause conflicts. Use wipefs to clear previous filesystem signatures:

wipefs -a /dev/sdX

 

Repeat for both drives, replacing /dev/sdX with the actual device paths.

 

Troubleshoot the Unraid GUI Issue
*Use web UI terminal coamnds for testing:
 

Error Logs: The error messages (emhttpd: error: mkmbr and segfault at 628) indicate the GUI might have a bug. Ensure you are on the latest stable version of Unraid:

Check for updates in Settings > Update OS.

If you're already on the latest version, consider upgrading to the most recent beta if the release notes mention fixes for secondary pools.

Manual Formatting and Mounting as a Workaround: Since the GUI fails but the console works, follow these steps:

Format the Drives via Console

mkfs.btrfs -f /dev/sdX /dev/sdY

Replace /dev/sdX and /dev/sdY with your 20TB drive paths.

 

Mount the Pool Manually:

mkdir -p /mnt/poolname
mount -t btrfs -o defaults /dev/sdX /mnt/poolname

Add the Pool to Unraid Configuration:

Manually edit the /boot/config/disk.cfg file to add your pool. This might require advanced knowledge of Unraid’s configuration.

 

Consider ZFS If Problems Persist

If btrfs issues persist, ZFS might be more reliable. Steps to create a ZFS pool manually:

Install ZFS Plugin: Use the Apps section in Unraid to install the ZFS plugin.

Create the ZFS Pool

zpool create -f -o ashift=12 media_pool mirror /dev/sdX /dev/sdY

Mount and Use: Add the pool to Unraid via the GUI under the "Pools" section.

 

otehrwise unraid rollback?
Roll Back to a Stable Version: If the issue appeared after an upgrade, consider rolling back to a previous stable release.

 

Final Steps

Once the pool is created and functioning:

Set appropriate share settings to ensure the new pool is not treated as a cache. Go to Shares > Share Settings and set the correct storage pool for your media share.

Configure RAID1 redundancy if using btrfs

btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt/poolname

 

Ok you never guessed what it was .... silly me thought the pools work like the array in terms of layout. Apparently you can not have empty slots in a pool ... 🤦‍♂️

Well I knew it was nothing complicated because I was able to mount and use the disks via console, which made them invisible from the UI.
After only using 2 slots it worked like a charm. I don't like that fact the the error message is very abitrary and I couldnt find the fact very easily but now I do undertand  

 

Also I am using this pool as a separate media storage, so I disabled all cahcing and moving settings, which completely cuts the pool of from my array (which is only for system data)

That beeing said, I am realy looking forward that Unraid adds "Array" as a pool type so one can setup multiple Arrays with potentially multiple cache drives. 
One main reason I would love that, is because my main storage is on a Truenas vm and I only have system data (docker, small VM images, plugins, etc.) on my array, which gurantees a small resilvering time when one of my 500gb drives fails. Also I could go with double parity on the system files, which I don't need on my movie collection.

 

Thanks anyway