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On 9 Feb 2016 16:48, "Gordon Henderson" <gordon+lug@xxxxxxxxxx> wrote:
>
> On Tue, 9 Feb 2016, Tom wrote:
>
>> One of my backup drives has just gone dead. Going to get a pair of USB drives with the intention of somehow exposing the two as one so that I can take one away for safe keeping and then, when I plug it in it the current active one will be mirrored to it and then unmounted for taking out for safe keeping.
>> Anyone seen any scripts around to allow me to do this with relative ease?
>
>
> You can use Linux software RAID mirroring as the back-end to this. Not sure I recommend this way of keeping a backup though, however it can be done.
>
> Build the mirrored set, put your data onto it, then soft-fail the drive you want to remove, (mdadm --fail /dev/md1 /dev/path/to/removing/drive) remove it and store it.
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> System carries on.
>
> Plug in the drive and re-sync the mirror with the right mdadm command
>
> e.g.
>
> Â mdadm --add /dev/md1 /dev/path/to/removing/drive
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> wait for it to complete - watch -n cat /proc/mdstat then repeat the soft-fail & remove process.
>
> You might want to use /dev/disk/by-uuid/... to make sure you're using the right device.
>
> You can script that with a script fired off from the udev trigger when the system sees the drive.
>
> The huge downside of that, is that every sector on the in-use disk will be read and every sector on the updating disk will be written. It takes time and you need perfect drives all the time. (There is a bitmap option to mdadm that came make this quicker, but I think it only supports ext2/3 at present)
>
> Plan B would be to not use a mirror system but to have a separate filesystem on the removable drive and use rsync. With clever use of rsync you can store many days/weeks/months of data, depending on how much changes between backups. Again, scripts fired off from udev can do the copy. This is the way I copy my camera to my desktop - however I have a simple script, so I plug in the camera, run the script then unplug it.
+1 for rsync method. What I do.
Roly. :-)
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