Tjyylli

Is it possible to rsync my 3TB big hard drive to two external 2TB hard drives?

If so what would the command look like?

If not, can you think of another solution to sync 3TB of data to 2x 2TB drives?
The only way I can think of is to manually copy the files... but loosing all of rsync's power this way :(

Options include setting up the destination drives as a single volume (RAID, LVM, btrfs...), or running two rsync commands on subsets of the data on the 3TB drive.
The former option makes the job simple (there's only one target) but has the disadvantage that both drives must be connected to access the data.
The latter is a little more effort, since it is necessary to identify a set of folders that is less than or equal to 2TB in size, but allows access to the data on each target drive independently. The best way to construct the rsync commands, if the set of folders is more complex than a few on the root of the 3TB drive, is probably to make use of rsync's --exclude-from option.

1) Simplest way:

If the 3TB of data is in directories less then 2TB, simply use two rsync commands.

E.g.

3TB  --- Folder1 with 1½TB --> rsync ---> 2TB drive

         Folder1 with 1½TB --> rsync ---> 2TB drive

2) Alternative:

Or mount both 2TB drives as a single volume. E.g. with linear mode or a stripe or storage spaces. (Linear mode would concatenate both drives in a form of RAID0. A stripe would alternate between writing to them.)

3) Alternative:

Or mount the second 2TB drive in a folder in a volume on the first drive.

The previous answers are good but here is a little more detailed.
1) Using 2 drives separately (annoying but needed sometimes)

• Mount the 2 new drives


• First need to figure out space constraints. Use df -h to see size available on new drives


• in the folder with the data you want to transfer, use the du command to figure out what will go in what drive. easiest and most likely will be alphabetical


• 
  du -ch -d0 this will show space per top level folder. the -d0 is how deep to show. so change to -d1 to see top level folders and then sub level folders space.


• 
  du -ch -d0 [0-9a-tA-T]*/ This will show you space in top level folders only matching top level folders with the first character matching 0-9 or a-t or A-T. Find the letter that best suits your space requirements.


• Use the opposite in your rsync --exclude command. So in this case I would use rsync --dry-run -av --exclude '/[u-zU-Z]*/' source destination. Remove --dry-run if it looks good. The leading / is to signify top level folders only. Notice the 0-9 is gone because we want to match all of that. We are also now matching the opposite letters we searched du with.

2) Raid drives as raid0 with mdadm. Then run a normal rsync command. Just know these drives need to stay together and if separated the data is lost.