If you have named server on rhel and want to install and config slave bind server for backup your dns server, here this a simple step:

install bind (if not install yet), for RHEL it is easy to install bind you have to install this package using "rpm -Uvh" from dvd or using yum
- bind (includes DNS server, named)
- bind-utils (utilities for querying DNS servers about host information)
- bind-libs (libraries used by the bind server and utils package)
- bind-chroot (tree of files which can be used as a chroot jail for bind)
- caching-nameserver (config files for a simple caching nameserver)

edit named.conf and named.rfc1912.zones or copy from your master bind server to /var/named/chroot/etc/named.conf and /var/named/chroot/etc/named.rfc1912.zones

change your zone config to be a slave server for your zone:

zone "example.com" IN {
type slave;
file "slaves/yourzonefile";
masters { your master ip; };
allow-update { your master ip; };

change your named.conf in master server:

zone "example.com" IN {
type master;
file "yourzonefile";
also-notify { your slave server ip1; your slave server ip2; }

restart you bind server, when you edit zonefile you have to edit serial to notify slave server to known that zone data is outdate and refresh it with master server.

If you make raid for boot disk with linux software raid (mdadm) and one disk failed, this is how you have to do for replace failed disk and boot the system.

first if failed disk is first hard drive (sda for example) you have to make sure that mirror disk can boot so you have to setup grub on mirror disk (sdb)

mysystem# grub
Grub>device (hd0) /dev/sdb
Grub>root (hd0,0)
Grub>setup (hd0)

and check /etc/grub.conf on mirror disk (sdb) is set correctly

remove failed disk from raid device.

mysystem#mdadm --manage /dev/md0 --fail /dev/sdb1 (up to your raid configuration)
mysystem#mdadm --manage /dev/md1 --remove /dev/sdb2

remove failed disk from all raid (md0,md1,md2 ..)

now shutdown the system and replace failed disk with new one.

reboot the system, if system is boot up without error you can add new disk to raid array.

make replaced disk (sda) the same partition like boot disk (sdb)

mysystem#sfdisk -d /dev/sdb | sfdisk /dev/sda

then add new disk to raid array

mysystem#mdadm --manage /dev/md0 --add /dev/sda1 (repeat for every partitions)

check raid status

mysystem#cat /proc/mdstat

wait until resync process is finish,if everything ok you can use the system.