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Re: Sync two disks and hot swap




On 11/08/17 02:49, Dominik George wrote:
Hi,

I have the following scenario:

  * A server with two hard drives in removable cases
  * A backup process writes data to both disks, making up a live backup server
  * A third disk is to be kept off-site
  * On a ergular basis, I want to hot-swap one of the disks, as in, remove
    one of the two synced disks and replace it with the stale off-site copy,
    and put the now recent copy off-site

I figure that a simple software RAID 1 would do the trick, but it is not
really made for it and would need some complex manual intervention in
order to not break the state on the removed disk.

Any ideas on how to achieve this, or arguments that RAID 1 would indeed
be a good solution?

Are the two drives in RAID (1?) or do they each have their own file system?


I have read articles about building a RAID 1 with three drives, migrating in data, pulling one drive and placing it off-site, operating in degraded mode on two drives, and then periodically re-installing the third drive, resilvering, pulling one drive and placing it off-site, and returning to degraded operations on two drives. But STFW just now, I see a lot of posts with titles indicating this is a bad idea.


I have three drives in mobile dock drawers, each with LUKS and ext4. One is on-line in my backup server, one is near-site, and one is off-site. Periodically, I put the near-site drive into the backup server, rsync the on-line drive to the near-site drive, remove the near-site drive, and then swap the near-site and off-site drives. Admittedly the wear is uneven, but it's KISS and it works.


But what I really want is some form of snapshot technology (rsync/hard link, LVM, btrfs, ZFS) with all the goodies -- realtime compression, realtime de-duplication, and encryption. I need a more powerful backup server (many core processor with AES-NI, 16+ GB RAM, SSD caches, etc.).


David