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Do you mean BIOS doesn't see drive at all, or it just won't boot from it?

Unraid is already immutable. The installed version isn't modified since it is loaded fresh into RAM from archives on the boot device at each boot. Internal boot device is counted as a drive. If you use a drive much larger than needed for the boot device, it can be partitioned into boot and pool partitions, then the pool partition can be used for other things like cache, dockers, ...

Attach Diagnostics ZIP to your NEXT post in this thread.

actually came from the parity calculation by reading all other array drives including parity. Parity by itself has none of your data. While you could technically format the 10TB as an Unassigned Device, might as well wait until after it is assigned during New Config. Assign new 10TB when doing New Config, then format it after starting the array. You can do the format during or after parity build.

Attach Diagnostics ZIP to your NEXT post in this thread. Setup Syslog Server.

Might be good to disable Docker in Settings until things are working well You need to clean this up anyway Sep 25 08:00:39 unRAIDVM root: Fix Common Problems: Warning: Share appdata set to cache-only, but files / folders exist on the arrayAnd your system share is on the array so that needs to be cleaned up too.

Nothing can move or delete open files so you have to go to Settings and disable Docker and disable VM Manager before you can work with those shares.

Single parity should be enough for so few array drives. You have some FCP errors and warnings you need to take care of: Sep 24 18:16:24 WOODOMUR root: Fix Common Problems: Warning: Deprecated plugin ca.mover.tuning.plg Sep 24 18:16:26 WOODOMUR root: Fix Common Problems: Error: Invalid folder cache contained within /mnt Sep 24 18:16:31 WOODOMUR root: Fix Common Problems: Warning: Share docker set to use pool cachepool, but files / folders exist on the cachhe pool Sep 24 18:16:31 WOODOMUR root: Fix Common Problems: Warning: Share system set to use pool cachepool, but files / folders exist on the cachhe poolYou should probably remove mover tuning at least until you get the other things taken care of. That version is too out-of-date to upgrade anyway. The invalid folder cache is a serious problem so it is flagged as an error. You don't have a pool named cache, instead it is named cachhe. But something is writing to the path /mnt/cache, probably some container host mapping. Since that path isn't actual storage, it is a path in rootfs, the RAM reserved for the OS. Since it is RAM, anything stored there won't survive reboot. And if you fill up that space by writing to it, it can cause problems for the OS since it will have no space to work with. The docker and system shares need to be on one pool or the other. Possibly you have duplicates you will need to clean up.

As you can see if you mouseover the download link, it should be .exe file. Make sure your browser isn't blocking the download.

You shouldn't even try to run any computer unless memory is working perfectly. Everything goes through RAM, the OS and other executable code, your data, everything. The CPU can't do anything with anything until it is loaded into RAM.

The only acceptable result for memtest is no errors.

So 4 drives sharing a single USB connection, and another 4 drives sharing another single USB connection. I think it likely that parity will only complicate things for you. And parity is not a substitute for backups anyway. Do you have good backups?

Tell us more about these enclosures. Can you post a link to the product?

How are these "enclosures" accessed by the computer? USB or SATA or SAS?

You should be able to examine most of your config in a text editor. super.dat (array assignments) is not simple text, and many plugins will have .txz files in their folders, but the .cfg files at the top of config on the flash drive should be simple text. See if any look corrupt.

Looks like you are having connection problems with that drive. In fact, I don't even see a SMART report for that device, so it must have completely disconnected. Check connections, both ends, SATA and power, including splitters.

Parity does not contain any of your data. A single parity drive provides redundancy for all array drives. Parity is basically the same concept wherever it is used in computers and communications. Parity is just an extra bit that allows a missing bit to be calculated from all the other bits. It is a very simple calculation. See here: https://docs.unraid.net/unraid-os/getting-started/what-is-unraid/ Then expand the Software-defined NAS section, then expand the How Parity Works section

You should have added it to the pool then reformatted. Now that it is in the pool try formatting it.

You can have one or two parity. They are independent, and each must be a single drive at least as large as the largest single data drive. You mention an enclosure and adding another. USB not recommended for assigned drives for many reasons.

Do you have an attached keyboard and monitor? Can you access the Unraid command line?

https://docs.unraid.net/unraid-os/system-administration/maintain-and-update/changing-the-flash-device/#backing-up-your-flash-device

https://docs.unraid.net/unraid-os/system-administration/maintain-and-update/changing-the-flash-device/#recovering-from-a-failed-boot-device-without-a-backup

Is that folder a ZFS dataset?

The filesystem on Unraid v5 was ReiserFS. It is no longer supported but it will still work in V6. In order to convert to XFS (recommended for array), and btrfs or ZFS (recommended for cache), you have to copy the data somewhere and reformat each disk.

Do you have a flash backup?