I was swapping over my graphics cards and may have knocked something in the case but after a couple of reboots (changing vfio settings), my system died.

 

A HDD failed, which I am in the process of rebuilding onto a new matched drive so that part is ok..

 

My cache drive also seemed to drop out of existence. After checking cables etc it seems to have reappeared as an unmounted drive. If I stop the array I have the option of selecting it as the '._cache' or 'cache' drive.

 

I have not noticed the '._cache' option before.... Either one tells me that the drive does not have a file system and so needs to be formatted.

 

My app data is backed up so it is not the end of the world, but I am confused about the two locations and if there is anyway to recover what was on the cache it would be appreciated.

 

Google doesn't really bring anything up for ._cache so here I am 🙂

 

 

The only thing I can guess from your post is that you're a Macintosh user because that's where files and directories with names beginning with dot-underscore come from. They are safe to delete - macOS will create them again if it needs to. For the rest, you'll need to post your diagnostics.

I am a Mac user and have restored my flash drive a couple of times from backups on my Mac but it is a location being offered by unraid not a file as below in the image. 
 

I will have a look at the flash drive and see if it is shown on there somehow ?

The same happened to me when restoring a backup of the USB thumb drive on a Mac using the Unraid USB creator tool. 

To fix it, just go into 

/boot/config/pools

on your USB drive and delete the ._cache file, then reboot.