Re: add another disk to existing raid 0, ie grow raid 0 possible?

[Nikolay Kichukov <hijacker@oldum.net>]

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Hello Neil,

Here goes the details. Once again, no valuable data, just curious what has gone wrong in that case:

dmesg output, first I stopped md2, then assembled it again to perform the grow.
http://pastebin.com/HkPVEKad

mdadm -E output:
http://pastebin.com/pJCjvrJE

The system runs GNU/Debian testing with latest updates from security-testing applied.
Kernel: 3.1.0-1-amd64
mdadm:  3.2.2-1

Let me know should you need any further information.

Cheers,
- -Nik

On 01/26/2012 12:57 PM, NeilBrown wrote:
> On Thu, 26 Jan 2012 10:47:14 +0000 Mathias Burén <mathias.buren@gmail.com>
> wrote:
> 
>> On 26 January 2012 10:26, Nikolay Kichukov <hijacker@oldum.net> wrote:
> Hi all,
> 
> I tried to expand md block device raid level 0 ( /dev/md2 ) by adding another partition to it.
> 
> Here are the steps:
> 
> mdadm --assemble /dev/md2
> mdadm: /dev/md2 has been started with 2 drives.
> hanna64:~# mdadm --grow /dev/md2 --raid-devices=3 --add /dev/sdc2
> mdadm: level of /dev/md2 changed to raid4
> mdadm: added /dev/sdc2
> mdadm: Need to backup 3072K of critical section..
> 
> 
> Now fdisk -l cannot complete, just goes to D state.
> 
> Disks layout before the grow attempt:
> 
> ARRAY /dev/md2 metadata=1.2 name=hanna64:2 UUID=4840f7f0:71b5f4a0:c4d8a42c:0b43b5fb
> 
> /dev/sda2: UUID="4840f7f0-71b5-f4a0-c4d8-a42c0b43b5fb" TYPE="linux_raid_member" LABEL="hanna64:2"
> UUID_SUB="cf97412f-269a-f3e8-fde2-8ca3bf42a349"
> /dev/sdb2: UUID="4840f7f0-71b5-f4a0-c4d8-a42c0b43b5fb" TYPE="linux_raid_member" LABEL="hanna64:2"
> UUID_SUB="9aee2d4c-6deb-911a-d790-cbd12f6c671c"
> 
> md2 : active raid0 sda2[0] sdb2[1]
>      15628288 blocks super 1.2 512k chunks
> 
> 
> Disk /dev/md2: 16.0 GB, 16003366912 bytes
> 2 heads, 4 sectors/track, 3907072 cylinders, total 31256576 sectors
> Units = sectors of 1 * 512 = 512 bytes
> Sector size (logical/physical): 512 bytes / 512 bytes
> I/O size (minimum/optimal): 524288 bytes / 1048576 bytes
> Disk identifier: 0x7b88c100
> 
> Disk /dev/md2 doesn't contain a valid partition table
> 
> 
> This array was used as swap, so no valuable information is stored there anyways. Let me know what has gone wrong and
> what I typed wrong assuming the grow command will just add /dev/sdc2 to the existing array and make it larger with the
> size of /dev/sdc2.
> 
> Thank you,
> -Nikolay Kichukov
> 
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>>
>>
>> AFAIK growing raid0 is not possible.

> Seems an odd thing to say, given that when OP demonstrated that mdadm
> didn't complain, but went as far as converting the array to RAID4 so it could
> perform a reshape.....

> It wasn't possible once, but times change.

> To know what went wrong I would need lots more details.
> Start with the output of 'dmesg' - or equivalent from logs
> (e.g. /var/log/kern.log or /var/log/messages).

> Then "mdadm -E" output of each device in the array.

> NeilBrown
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