Thisisalloneword,   The drive can report smaller if it was configured that way, without using the whole drives space. Do you have any other Virtual Disks on the contoller, and if so is the drive in question listed in both Virtual Disk? That would explain that, as far as the issue you're seeing, I would start with makeing sure the server is up to date on BIOS, iDrac, Raid Controller, and the drives.  I wouldn't think that you would need to replace anything as of now, I would update and then see if the reporting on the drives changes and identifies an issue. You may also want to screenshot the Virtual Disk page, as well as the Physical Disk page.   Let us know what you see.
The machine has been running CentOS 7 fine for almost a year. But I noticed some weird disk issue with /dev/sdb1 . Many files had ????? on them and the OS gave input/output error when trying to access them. So I tried to reboot it in hopes that would fix it. But now it won't boot up. It takes me to this message on the console about "no controller found". I am not even sure what a controller is? Any tips on how to debug further? I suppose I can just buy the drives to replace, but not sure which model/sizes to get or how many? [IMAGE][IMAGE]  
No controller found on Poweredge M630 running CentOS 7 - Disk failure?