Mdadm

stop raid device

# mdadm -S /dev/md2

when a raid 5 or 6 fail you have to rebuild using latest version of data :

get events of drives

# mdadm --examine /dev/sd[abcgf]2 | grep Event
         Events : 11369
         Events : 11369
         Events : 11369
         Events : 34
         Events : 34

force rebuild raid without the 2 latest drives

# mdadm -Af /dev/md2 /dev/sda2 /dev/sdb2 /dev/sdc2

then add back 2 bad drives

# mdadm -a /dev/md2 /dev/sdg2 /dev/sdf2

watch rebuild

# watch -n1 "cat /proc/mdstat"
...