Is all physical disk on your system healthy? Can you go to controller utility and check status of physical disk and virtual disks. You can find more details on preserved cache and this error from below links

https://www.dell.com/support/manuals/en-us/poweredge-rc-h730p/perc9ugpublication/managing-preserved-cache?guid=guid-3a82d9bf-1ad7-4229-bdf2-fdeeec45045d&lang=en-us

https://www.dell.com/support/manuals/en-us/poweredge-rc-h730/perc9ugpublication/offline-or-missing-virtual-drives-with-preserved-cache-error-message?guid=guid-38104ed7-371d-4712-a6d5-35cf3041b9f4&lang=en-us 

I'm not 100% sure on that. This server is new to me so I didn't know much about it. I do have some additional pictures as well.