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

[NeilBrown <neilb@suse.com>]

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On Thu, Jul 13 2017, Ram Ramesh wrote:

> I am trying to shring my mdadm underlying disks/partitions as a way of 
> reclaiming space after md shrink operation. Here is my md
>> Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] 
>> [raid4] [raid10]
>> md0 : active raid6 sdb1[6] sdg1[11] sdd1[12] sdf1[8] sde1[9] sdc1[10]
>>       12348030976 blocks super 1.2 level 6, 64k chunk, algorithm 2 
>> [6/6] [UUUUUU]
>>       bitmap: 2/23 pages [8KB], 65536KB chunk
>>
>> unused devices: <none>
>
> Here is my mdadm detail about /dev/sdb1
>> Avail Dev Size : 11720780943 (5588.90 GiB 6001.04 GB)
>>      Array Size : 12348030976 (11776.00 GiB 12644.38 GB)
>>   Used Dev Size : 6174015488 (2944.00 GiB 3161.10 GB)
> I fail, remove and repartition /dev/sdb1 so that new partition table 
> looks like this. (No change to data obviously)
>>    New partition table:
>>    Number  Start (sector)    End (sector)  Size       Code  Name
>>        1            2048      6442452991   3.0 TiB     FD00  Linux RAID
>>        2      6442452992     11721045134   2.5 TiB     FD00  Linux RAID
>
> Since new /dev/sdb1 is significantly bigger than what mdadm says that it 
> is using, I thought I could simply re-add the drive. However, I get
>> sudo mdadm /dev/md0 --re-add /dev/sdb1
>> ***mdadm: --re-add for /dev/sdb1 to /dev/md0 is not possible***
> Why? What did I miss here? Is it possible to fix this so that I can 
> repartition other drives and -re-add them without having to go through 
> full rebuild after each change?

Please report output of "mdadm --examine" on both a device that is active
in the array, and the device that you are trying to add.
Also "mdadm --examine-bitmap" of a device that is active in the array.

NeilBrown

>
> I researched as much as I could on the net and came up with nothing 
> except some one saying that mdadm keeps something at the end of the disk 
> regardless of what it says about "Used Dev Size." Is it possible to move 
> this info so that I could re-add?
>
> Ramesh
>
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