If one of your drives have failed in a dell server probably with a E1810 Error , you will need to replace the drive.To skip the error and allow the server to boot and Bypass :

There are offline or missing virtual drives with preserved cache. Please check the cables and ensure that all drives are present.

Press Ctrl R to go to the PERC Bios, clear the cache in the PERC BIOS. To clear the cache, you navigate to the screen that has the tree structure of disk groups and virtual disks. Then navigate by up-arrow until you are on the root of the tree structure, which will be the PERC H710 Mini and not a specific disk group. Press F2 which gets you to a screen that allows you to manage the cache. That will allow you to clear the cache.

Exit by hitting ESC and then control-alt-del to reboot.