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What is bare-metal restore?

A bare-metal restore (BMR) is the process of rebuilding a complete server, including its operating system, applications, settings and data, onto hardware with nothing installed, from an image backup of the whole disk. It replaces manual reinstallation, but it works only if an image exists and the recovery media, drivers and keys are ready.

How does image-level recovery differ from file recovery?

A file-level backup preserves data but not the system around it. After a server is lost, the operating system and every application have to be installed by hand before any files can come back. An image backup captures the whole disk block by block, including the partition layout and boot configuration, so writing it back reproduces the server as it was at that moment. A backup agent running on the server is the usual way to capture an image of a physical machine.

What is the re-imaging sequence?

  1. Boot from recovery media. The empty machine starts from a USB drive, a disk image or a network boot that carries a small recovery environment.
  2. Connect to backup storage. The recovery environment loads network and storage drivers and connects to the repository holding the image.
  3. Choose a restore point. After ransomware this is the last point known to be clean, not simply the newest.
  4. Recreate the disk layout. Partitions and volumes are created to match the original, or resized when the new disks differ in size.
  5. Write the image. The disk contents, including the boot records, are copied from storage onto the new volumes.
  6. Adjust for new hardware. If the replacement machine differs from the original, drivers for its storage and network controllers are added to the restored system.
  7. Restart and verify. The machine boots into the restored operating system, and services and data are checked before it rejoins the network.

What sits outside the image?

Several dependencies sit outside the image itself. Recovery media has to exist and match the backup software version. Drivers for replacement hardware are needed when the original hardware is gone. Disk encryption keys have to be reachable from somewhere other than the lost machine. Directory services that the recovery tools sign in against may need restoring first.

Why does scale change the picture?

Restoring one server in a test says little about restoring dozens at once, when every rebuild reads from the same backup storage. Read speed on the repository becomes the limit, so the figure that matters is restore throughput with many rebuilds running in parallel. Images held as an immutable backup survive an attack that destroys the original servers, and rebuilding inside a clean room recovery environment keeps a restored machine off the production network until it has been checked.

Frequently asked questions

Is bare-metal restore the same as disaster recovery?

No. It is one technique used within disaster recovery: rebuilding individual machines from images. Disaster recovery also covers sites, networks and the order in which services return.

Can a bare-metal restore go to different hardware?

Yes, if drivers for the new hardware are added during the restore.

What backup does it need?

An image backup of the whole disk. File-level backups do not contain the operating system and boot configuration.