Hello,

As a first step I upgraded my cache drive from SSD to a bigger SSD. I messed around with the docker image file so I had to reinstall all my apps, but in the end it worked fine.

Then I installed a PCI-E to SATA expansion card to reach higher speeds for the cache drive.

At first Unraid quickly recognized the cache drive and assigned it to its role. The apps went up so I thought it was ok.

But then the failures came. Unable to update docker apps and Sabnzbd unable to complete downloads. Sometimes saying it is unable to write sometimes writing some 40 Gb of files and all of a sudden all the files already written are cleaned up so the job is unable to complete.

I got this message while trying to update Sabnzbd: 

Error: open /var/lib/docker/tmp/GetImageBlob522948715: read-only file system

 

Any idea?

novanas2-diagnostics-20190723-0843.zip

There are what appear to be connection issues with the SSD, replace both cables.

 

Possibly because of that cache filesystem is corrupt, you'll need to backup and re-format.

You are getting write errors on the cache drive which is worrying.   Not sure if this is just a cabling problem or a genuine problem with the drive.    As a result the file system on the cache drive is corrupt and your docker image file is corrupt.

Ok. I will try that. Thank you both

Good guess.
I connected the cache SSD drive to the new PCI-E controller with an old SATA cable. 
I now used another SATA 6Gb/s cable I had around and it seems to work fine.
I should have known better, being a professional in audio-video systems I know the importance of HDMI cable versions.