Simon said on Tue, 11 Jul 2023 22:05:26 +0100

>Thinking a bit more about this, there is another way to do it which
>may be useful if your backup is on slow media (such as a USB-2 drive) :
>
>1) On md2, fail one drive (I’ll use drive 2 here), then remove it from
>the array, then remove the raid metadata from it (three md commands
>that I wouldn’t even try and recall from memory !)
>
>You now have your data still on drive 1 in the original md2 array
>which now only has one drive in it (and hence no redundancy).
>
>2) delete drive 2 part 2, create new parts 2 & 3 on drive 2
>
>3) create a new md2 array (it needs to have a different name). You
>need to explicitly tell it two drives and there’s an option to say a
>drive is missing. Ditto with a new md3 array.
>
>You now have your new arrays set up. You can mount them wherever you
>want so you can copy your data to them.
>
>4) Copy your data from the original md2 with your preferred tool -
>some prefer cp, I prefer rsync, some will use mv, some will …
>
>You now have your data on the new arrays.
>
>5) unmount and stop the original md2, and remove the raid metadata
>from drive 1 part 2
>
>6) delete drive 1 part 2, create your new partitions to match those on
>drive 2
>
>7) Add the new partitions to the relevant arrays. md will now rebuild
>the array by copying data from the existing partition to the one just
>added. You can check progress with cat /proc/mdstat. You can also use
>the arrays while they are rebuilding, but system performance is
>degraded (there’s tuning options if that’s a problem, but generally it
>isn’t).
>
>8) Unmount your new arrays from their temporary locations, and mount
>them where they should be. Update stab, and rebuild your initramfs.

You just reminded me why I don't use RAID.

SteveT

Steve Litt
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