Q: Why is my RAID array degraded when all the drives report they are online, none of them are missing or appear to be bad?
A: Usually when a drive is bad it just dies, cannot be fixed or used and it is clear you must replace it. There are a lot of things that can cause temporary conditions that can degrade an array, high temperature is a common one, insufficient power supply is another.
This situation is typical when a drive has not completely died but has failed to respond in a timely fashion for some reason.
Timeout Recover Setting in XigmaNAS. XigmaNAS use 15sec hw.ata.to value as default and applay for any *ATA drives. You can change the default value at System > Advanced > sysctl.conf if needed.