I have searched on this and am not getting useful results. Other threads talk about changing the format type for the cache, but I can't seem to find where to change that setting.

 

I have 4 drives in my main array and a single cache drive.  I have a basic license key.

 

When I try to add a second cache drive (brand new, unused), the new one says that its part of a cache pool, and the original one says that it cant be mounted.

 

It wants to format the disk.  I give it permission and it goes through the motions of formatting the disk, but them gives the same result.

 

Am I running into a number of devices limit?  I didn't think the flash drive counted as one of my 6 devices.

 

If I go back to a single cache drive, all is well.

I figured it out.

 

Since my single was formatted XFS it was confused.

 

So here is what I did, since there was nothing on my cache volume I wanted (I moved it all to the array before trying this)

 

Stop the array.

Find the offending drive and click its link.

Change file system type from auto to btrfs (or btrfs-encrypted) and hit apply

Start the array

WHen it asks to format, do it.

Poof.  All good now.

 

 

Now to move things back to the cache from the array.