When predictive failure happens, it is recommended to replace the corresponding disk/drive in the RAID array.
RAID Event logs show Controller ID: 0 PD Predictive Failure: Port X – X:X:X warnings although the disks and virtual drives are online/optimal.
Predictive Failure (ID 96) might be seen in the RAID logs.
It is recommended that you back up your RAID array and replace the drive as early as possible.
Predictive failure happens when specific Self-Monitoring Analysis and Reporting Technology (SMART) attributes of a drive reached a predefined threshold (varies by drive/disk manufacturer). This is typically an indication or warning that the corresponding drive may fail in the near future even though it is still functional at the moment.
It is possible that there are internal errors on a disk, which could eventually worsen its state and that of the virtual drive it belongs to.