In this example we have 2 drives in a RAID array and /dev/sdb is the one that failed.  /dev/sda1 is also the /boot partition which we tell grub to install on /dev/sdb eg install root (hd0,0) /dev/sda1 on the new drive /dev/sdb (hd1)
 

First copy the partition table from /dev/sda to /dev/sdb

dd if=/dev/sda of=/dev/sdb bs=512 count=1

Run partprobe to detect the new partition table
partprobe

Add the partitions of the replacement drive /dev/sdb back to the array


mdadm --manage /dev/md0 -a /dev/sdb1
mdadm --manage /dev/md1 -a /dev/sdb2
mdadm --manage /dev/md2 -a /dev/sdb3
 

Install grub on the new drive
grub
root (hd0,0)
setup (hd1)

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