Thank you Roman, the array-size parameter is just what I needed. After
2 rebuilds I've got everything just as I want it now.
It still doesn't make sense to me why array-size was required, even
after reading the man page. However the array-size parameter appeared
to shrink the array temporarily which for some reason allowed the
reshape of the array to work down to 4 devices.
Since then I was able to re-expand the filesystem, do some filesystem
checks and get everything mounted again. Thank you again!
On Sat, Jan 19, 2019 at 4:09 PM Andreas Klauer
<Andreas.Klauer@xxxxxxxxxxxxxx> wrote:
>
> On Sat, Jan 19, 2019 at 09:52:11PM +0500, Roman Mamedov wrote:
> > Read `man mdadm` for --size. What you need is --array-size.
>
> mdadm should even be nice enough to provide the exact size required
> to make the operation.
>
> | # mdadm --grow /dev/md42 --raid-devices=4
> | mdadm: this change will reduce the size of the array.
> | use --grow --array-size first to truncate array.
> | e.g. mdadm --grow /dev/md42 --array-size 5860011008
>
> (This is just an example.)
>
> You have to be really, really sure your filesystem does not exceed
> the new size.
>
> I think mdadm actually accepts G units here, so if you did
> a resizefs 2345G you can use --array-size=2345G as well
> (and mdadm will still complain if it's not small enough
> when trying to reduce number of devices afterwards)
>
> Why not switch to RAID-5 instead?
>
> Regards
> Andreas Klauer
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Eric C. Pulvino
cell: 919.592.5995
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