How to avoid data loss when rebuilding a RAID set

Be very carefull when rebuilding a RAID set. 

We have seen if a drive fails after a few years of use, the other drives are also at risk.

This means, when you rebuild, there is a higher chance another drive will fail because all drives in a RAID set will be under heavy load for a long time during the rebuild.

So, our advise it to take a backup before rebuilding:

• RAID 1: only 1 drive can fail, so take a backup before rebuilding
• RAID 5: only 1 drive can fail, so take a backup before rebuilding
• RAID 10: if the second drive fails of the RAID 1 stripe, all data will be lost, so take a backup before rebuilding
• RAID 6: 2 drives can fail, backup is advised but not manditory