One of the primary benefits of RAID 1 mirroring is that it provides data reliability in the case of a single disk failure. When one disk drive fails, all data is immediately available on the other without any impact to the data integrity. In the case of a disk failure, you need to replace the defective drive and then rebuild the RAID again.
On the Raid 5, one drive can fail and it is possible to rebuild the data after replacing the failed hard drive with a new drive. The extra work of calculating the missing data degrades the write performance to the RAID 5 volume while the volume is being rebuilt.
For the RAID 6, you can remove and then put back again the degraded drive and try to rebuild it.
Finally, for the RAID 5, can you please tell us the status of the RAID? If this the status is offline you can try to do is create the RAID on the raid BIOS again, without initializing the drives. You have to take into consideration, that since the 4 drives are degraded the information might be lost.
We recommend checking the following documents for more additional information:
Intel Embedded Server RAID Technology 2 (ESRT2)
Rebuilding Degraded RAID Volume After Failed Drive Is Replaced
Intel® Server Products and SolutionsIntel® RAID Software User Guide for full featured andhttps://www.intel.com/content/dam/support/us/en/documents/server-products/raid-products/SWUG_full_featured_entry_RAID.pdfentry level RAID controllers.