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On 11/8/17 5:59 PM, David Christensen
wrote:
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
I have used raid 1 to make a drive I can take off site for
backup. You just grow the raid 1 array by one disk and add the
disk you want to take out (even on a usb/sata connection ... but
slow). Of course the disk or partition(s) need to be the same
size as the array. Let it sync and then boot to a live cd and you
can fail and remove that drive. Or just power down and remove
the drive. That way the embedded file system will be unmounted
correctly. I have then taken that one drive and connected it to
another system and been able to run the raid 1 in degraded mode
and mount the embedded file system(s) to get to the files. To
make the original raid happy just grow the array again setting the
number of drives back to what it was originally (you can grow to a
smaller number). The syncing can be slow since every byte on the
drive needs to be "synced" instead of just the space the files
take up.
I tried to use btrfs in several VMs running debian but I kept
having to delete snapshots to make sure I had enough free space.
--
...Bob
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