I have two identical hard disks (say HDD1 and HDD2) with 4TB capacities. I want to create install CentOS, update it, install services and create users on one of the hard disk, say HDD1, meant only for backup.

Now if I want to clone this on to HDD2 it takes a huge amount of time. So instead I would like to first create (almost) identical partitions and install CentOS of the same version installed on HDD1 and then rsync HDD1 onto HDD2 while booting from some live OS. Would this serve the same purpose of making a copy (though not a clone) of HDD1 on to HDD2 or would there be some issues that I should be concerned about? The copy is to be used only for back up purpose and nothing else.

Edit: The purpose also includes taking periodic backups for which rsync is being considered.

  • I almost thing I understand what you are asking, but it seems to me like a “6 of one, 1/2 a dozen of another” situation. Rsync will simply clone one disk to another to create a perfect copy. Preinstalling an OS on one will not speed anything up really if you think about it. Jun 26, 2016 at 3:16
  • Cloning takes a lot of time, after all it is 4TB! Where as the data size is much small, about 100G. Besides, the downtime of the service also will be minimal, and would need to be done only for the OS partitions, so downtime will be only for about 20GB for OS.
    – Quiescent
    Jun 26, 2016 at 3:25

2 Answers 2


rsysc will transfer your files, but won't do the same with your bootloader, your partitions, volumes (if any). Make sure, that you take care of that too.


If the second drive will strictly be used for backup and not as a live system, the best course of action is to use a cloning live CD to make an exact copy of the installation. This will ensure that you copy every sector and partition of your original installation. There are a number of open source live CD distributions that can accomplish this, and their transfer speed is pretty much only limited by the hardware bottleneck. You can also compress the cloned images and encrypt them, or send them through a network connection.

In addition, unless your OS drive has full hard drive encryption, the cloning software will recognize the file system and only copy actual data, not empty blocks. With that said, the time will only be as much as it takes to copy a few gigabytes, not all four terabytes.

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