Re: Why can't I re-add my drive after partition shrink?

[NeilBrown <neilb@suse.com>]

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On Wed, Jul 19 2017, Ram Ramesh wrote:

> Here is my attempt to repeat the steps in my last attempt to remove, 
> repartition, re-add. Last time I did it on /dev/sdb. Now I am going to 
> do it on /dev/sdc. Note that I have not been successful as you see at 
> the end. I am going to keep the array degraded so that I can still get 
> old info from /dev/sdc1, if you need anything else. I will keep it this 
> way till tomorrow and then add the device for md to rebuild. Please ask 
> anything else before that or send me a note to keep the array degraded 
> so that you can examine /dev/sdc1 more.

Thanks.  I *love* getting all the details.  You cannot send too many
details!

This:
> <good device still in md0>
>> zym [rramesh] 265 > sudo  mdadm --examine /dev/sdb1
>> /dev/sdb1:
..
>>  Avail Dev Size : 6442188800 (3071.88 GiB 3298.40 GB)

and this:

> <device just removed and repartitioned>
>> zym [rramesh] 267 > sudo mdadm --examine /dev/sdc1
>> /dev/sdc1:
...
>>  Avail Dev Size : 11720780943 (5588.90 GiB 6001.04 GB)

Shows the key difference.  "Avail Dev Size", aka sb->data_size, is
wrong.  We can fix it.

>
> <Cannot re-add!!!!>
>> zym [rramesh] 270 > sudo mdadm /dev/md0 --re-add /dev/sdc1
>> mdadm: --re-add for /dev/sdc1 to /dev/md0 is not possible

Please try
   sudo mdadm /dev/md0 --re-add /dev/sdc1 --update=devicesize

Thanks,
NeilBrown

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