What is Relax and Recover(ReaR) and how can I use it for disaster recovery?

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Package: rear

Issue

  • Red Hat Enterprise Linux now contains Relax and Recover(ReaR) which can be used for image based backups. What is it? Any example for using this backup utility?

Resolution

What's Relax and Recover

Relax-and-Recover(ReaR) is a recovery and system migration utility. The utility produces a bootable image and restores from backup using this image. It also allows to restore to different hardware and can therefore be used as a migration utility as well.

Rear package is now available for Red Hat Enterprise Linux:

How to set up ReaR to backup with NFS method

Before setting up ReaR, you need to make a backup-restore plan according to your environment. In this tutorial, we will:

  • Set up an NFS server for holding the backup files.
  • Back up the files to the NFS server and store the disaster recovery system to an ISO image.
  • Boot the restore server with disaster recovery system and finish the recovery.

Detailed steps are as follows:

  1. Create an export on the NFS server(in this example, it has the IP address 192.168.56.1). We use /storage directory for storing the back up files later.

    # yum install nfs-utils

# mkdir /storage

# cat /etc/exports
/storage        *(fsid=0,rw,sync,no_root_squash,no_subtree_check,crossmnt)

# service nfs start

  2. Install packages which are required for creating ISO image on the backup server.

    # yum install rear genisoimage syslinux

  3. Modify the configuration file /etc/rear/local.conf on the backup server with these settings.

    # cat /etc/rear/local.conf
OUTPUT=ISO
OUTPUT_URL=nfs://192.168.56.1/storage
BACKUP=NETFS
BACKUP_URL=nfs://192.168.56.1/storage
BACKUP_PROG_EXCLUDE=("${BACKUP_PROG_EXCLUDE[@]}" '/media' '/var/tmp' '/var/crash')
NETFS_KEEP_OLD_BACKUP_COPY=

    Be careful when changing the BACKUP_PROG_EXCLUDE variable. Always preserve the default excludes to avoid issue described in solution RHEL 7 restored from ReaR doesn't boot if custom backup excludes were used for backup.

  4. Create the disaster recovery system and generate backup files.

    # rear -d -v mkbackup

    Rear will examine the current backup system and gather necessary information, like the disk layout, files to be excluded and the boot loader, etc. Then a bootable ISO image with disaster recovery system will be created under /var/lib/rear/output by default. At last the files to be backed up as well as the bootable ISO image will be transfered to the NFS server.

  5. Recovery test.
    5.1 Burn the bootable ISO image to a CD or DVD.
    5.2 Boot the test server from the recovery medium.
    5.3 Select Recover <hostname>. Here, the hostname is the backup server's name.
    5.4 Login as root without password.
    5.5 Recover the backup to this test server:

    # rear -d -v recover

    5.6 After restoring the backup, you may choose to stay in the shell of the disaster recovery system to check the recreation on the test server. If everything is okay, reboot the test server and starts from local harddisk.
    TIPS:You can also choose the Automatic Recover <hostname> to automate the recovery process, as long as no error occurs when you manually recover the test server.

  6. In case a disaster has occurred, you can proceed recovery steps as described in Recovery test section on a server which has been tested and has the same hardwares as the backup server.

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