Never replace a failed drive with a drive that was part of a previous RAID system; always zero out the replacement drive before using it. If the drive is making unusual mechanical noises, turn it off immediately and get assistance. Just as in the physical server environment, leaving a mechanically failing drive powered on increases the likelihood of further damage and significantly reduces the chances of a full recovery.
Tip: Label the drives with their position in a RAID array before removing them from your system.
If a RAID system fails in the middle of a rebuild process, do not run further rebuild attempts. Never migrate VMs to or from a suspect RAID, and if you do need to shut down or power cycle your RAID hardware, ensure all virtual machines and VMware hosts are gracefully shut down first.