I‘m using rsnapshot filesystem snapshot utility to make incremental snapshots of local and remote filesystems for 10 production servers running on RHEL 5.x system. The rsnapshot commands makes extensive use of hard links, so if the file doesn’t change, the next snapshot is simply a hard link to the exact same file. How do I use the rsync command to copy my the entire snapshot directory /raid6/rsnapshot/ (around 4TB) to a remote server for mirroring purpose?

The rsync command can preserve hard links and make the exact copy of /raid6/rsnapshot/ directory to a remote server using the following syntax. This is useful for making offsite backups or copy existing backups to a usb hard disk:

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rsync -az -H --delete --numeric-ids /path/to/source server2:/path/to/dest/

OR

rsync -az -H --delete --numeric-ids /path/to/source 192.168.1.5:/path/to/dest/

OR

rsync -az -H --delete --progress --numeric-ids /path/to/source 192.168.1.5:/path/to/dest/

Where,

1. -a : Archive mode (i.e. recurse into directories, and preserve symlinks, file permissions, file modification times, file group, file owner, device files & special files)
2. -z : Compress file data during the transfer
3. -H : Preserve hard links (i.e. copy hard links as hard links)
4. --delete : Delete extraneous files from the receiving side (ones that aren't on the sending side), but only for the directories that are being synchronized i.e. keep exact replica of your /raid6/rsnapshot directory.
5. --numeric-ids : Transfer numeric group and user IDs rather than using user and group names and mapping them at both ends.
6. --progress : Show progress during transfer.

Rsync copy hard links

In short type the following command as root user to copy /raid6/rsanpshot to another backup server named backupserver2:
# rsync -az -H --delete --numeric-ids /raid6/rsanpshot backupserver2:/backups/
You can pull backups too from backupsrver2 as follows:
# rsync -az -H --delete --numeric-ids backupserver1:/raid6/rsanpshot /backups/
Smaller size directories can be dumped to usb 2.0/3.0 or eSata external hard drives using the same syntax. First, mount usb hard drive:
# mount /dev/sdXY /mnt/usbdisk
Next, use the rsync command as follows:
# rsync -az -H --delete --numeric-ids /raid6/rsanpshot /mnt/usbdisk/