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

On Thu, 26 Jan 2012 10:47:14 +0000 Mathias Burén [off-list ref]
wrote:

On 26 January 2012 10:26, Nikolay Kichukov [off-list ref] wrote:

quoted

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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