The RAID 5 can cope with one of the disks failing. I would advise that you check the front of the server and ensure the drive bay has a red or warning light lit up and pull the drive out with the light indicated and replace it.
If it would make you feel better to contact your sys admin or someone similar then that's okay but I would avoid leaving this an unreasonable amount of time as if the drive fails completely, then another does too then your array will catastrophically fail.
Additionally, in my experience (especially DL ranges) HP servers can have a tenancy to be fussy about the drive and kick it out after a few days leaving you back in the same situation. For the avoidance of any doubt I strongly advise using a HP certified or branded disk, this is usually indicated by the presence of a small square HP sticker with a small barcode on the top of the disk.