Chapter 18. Recovering and restoring a system
To recover and restore a system using an existing backup, Red Hat Enterprise Linux provides the Relax-and-Recover (ReaR) utility.
You can use the utility as a disaster recovery solution and also for system migration.
The utility enables you to perform the following tasks:
- Produce a bootable image and restore the system from an existing backup, using the image.
- Replicate the original storage layout.
- Restore user and system files.
- Restore the system to a different hardware.
Additionally, for disaster recovery, you can also integrate certain backup software with ReaR.
Setting up ReaR involves the following high-level steps:
- Install ReaR.
- Modify ReaR configuration file, to add backup method details.
- Create rescue system.
- Generate backup files.
18.1. Setting up ReaR
Use the following steps to install the package for using the Relax-and-Recover (ReaR) utility, create a rescue system, configure and generate a backup.
Prerequisites
Necessary configurations as per the backup restore plan are ready.
Note that you can use the
NETFSbackup method, a fully-integrated and built-in method with ReaR.
Procedure
Install the ReaR utility by running the following command:
# yum install rearModify the ReaR configuration file in an editor of your choice, for example:
# vi /etc/rear/local.confAdd the backup setting details to
/etc/rear/local.conf. For example, in the case of theNETFSbackup method, add the following lines:BACKUP=NETFS BACKUP_URL=backup.locationReplace backup.location by the URL of your backup location.
To configure ReaR to keep the previous backup archive when the new one is created, also add the following line to the configuration file:
NETFS_KEEP_OLD_BACKUP_COPY=y
To make the backups incremental, meaning that only the changed files are backed up on each run, add the following line:
BACKUP_TYPE=incremental
Create a rescue system:
# rear mkrescueTake a backup as per the restore plan. For example, in the case of the
NETFSbackup method, run the following command:# rear mkbackuponlyAlternatively, you can create the rescue system and the backup in a single step by running the following command:
# rear mkbackupThis command combines the functionality of the
rear mkrescueandrear mkbackuponlycommands.
18.2. Scheduling ReaR
The /etc/cron.d/rear crontab file in the rear package runs the rear mkrescue command automatically at 1:30 AM everyday to schedule the Relax-and-Recover (ReaR) utility for regularly creating a rescue system. The command only creates a rescue system and not the backup of the data. You still need to schedule a periodic backup of data by yourself. For example:
Procedure
-
You can add another crontab that will schedule the
rear mkbackuponlycommand. -
You can also change the existing crontab to run the
rear mkbackupcommand instead of the default/usr/sbin/rear checklayout || /usr/sbin/rear mkrescurecommand. - You can schedule an external backup, if an external backup method is in use. The details depend on the backup method that you are using in ReaR.
The /etc/cron.d/rear crontab file provided in the rear package is considered deprecated, see Deprecated functionality shell and command line, because it is not sufficient by default to perform a backup.
18.3. Using a ReaR rescue image on the 64-bit IBM Z architecture
Basic Relax and Recover (ReaR) functionality is now available on the 64-bit IBM Z architecture and is fully supported since RHEL 8.8. You can create a ReaR rescue image on IBM Z only in the z/VM environment. Backing up and recovering logical partitions (LPARs) has not been tested.
ReaR on the 64-bit IBM Z architecture is supported only with the rear package version 2.6-9.el8 or later. Earlier versions are available as a Technology Preview feature only. For more information about the support scope of Red Hat Technology Preview features, see https://access.redhat.com/support/offerings/techpreview.
The only output method currently available is Initial Program Load (IPL). IPL produces a kernel and an initial RAM disk (initrd) that can be used with the zIPL boot loader.
Prerequisites
ReaR is installed.
-
To install ReaR, run the
yum install rearcommand
-
To install ReaR, run the
Procedure
Add the following variables to the /etc/rear/local.conf to configure ReaR for producing a rescue image on the 64-bit IBM Z architecture:
-
To configure the
IPLoutput method, addOUTPUT=IPL. To configure the backup method and destination, add
BACKUPandBACKUP_URLvariables. For example:BACKUP=NETFS BACKUP_URL=nfs://<nfsserver name>/<share path>
ImportantThe local backup storage is currently not supported on the 64-bit IBM Z architecture.
-
Optional: You can also configure the
OUTPUT_URLvariable to save the kernel andinitrdfiles. By default, theOUTPUT_URLis aligned withBACKUP_URL. To perform backup and rescue image creation:
# rear mkbackup-
This creates the kernel and initrd files at the location specified by the
BACKUP_URLorOUTPUT_URL(if set) variable, and a backup using the specified backup method. -
To recover the system, use the ReaR kernel and initrd files created in step 3, and boot from a Direct Attached Storage Device (DASD) or a Fibre Channel Protocol (FCP)-attached SCSI device prepared with the
ziplboot loader, kernel, andinitrd. For more information, see Using a Prepared DASD. -
When the rescue kernel and
initrdget booted, it starts the ReaR rescue environment. Proceed with system recovery.
Currently, the rescue process reformats all the DASDs (Direct Attached Storage Devices) connected to the system. Do not attempt a system recovery if there is any valuable data present on the system storage devices. This also includes the device prepared with the zipl boot loader, ReaR kernel, and initrd that were used to boot into the rescue environment. Ensure to keep a copy.
Additional resources
